NOVELTY - Preparation of oil removing agent, comprises: (1) processing the oil-containing sewage and sludge, and preparing oil removing bacteria; (2) mixing the oil removing bacteria strain; (3) using the mixed bacteria liquid for fermentation amplification culture in an industrial culture medium; (4) plate-and-frame press filtering through a hydraulic ferment; and (5) drying and crushing, to obtain the dry powder.    USE - The methods are useful for preparing an oil removing agent; and for treating an oil field sewage (all claimed).    ADVANTAGE - The method is high in biological activity, has a good oil removal effect, and fulfills the aim of high-efficiency oil removal, and the biofilm has high impact resistance; and the method for preparing the microbial inoculum has the characteristics of simple operation and low cost, and is suitable for large-scale production and application.    DETAILED DESCRIPTION - Preparation of oil removing agent, comprises: (1) taking the oil-containing sewage and sludge in the Jiangsu a set of oil field oil-containing sewage tank containing oil-containing sewage of oil field and the bacteria in the sludge on the Luria broth (LB) culture medium, neutral environment, 25-30 degrees C to enrichment culture, then separating, purifying and filtering to obtain 3 plant oil removing efficiency of oil removing bacteria, the 3 plant oil removing bacteria strain are as OFB-1: Bacillus cereus which is preserved in the China microorganism bacterial strain preservation management committee common microorganism center (CGMCC), the preservation date is August 15, 2011, and the preservation number is CGMCCNO. 5135; OFB-2: B. cereus which is preserved in the China microorganism bacterial strain preservation management committee common microorganism center (CGMCC), the preservation date is August 15, 2011, and the preservation number is CGMCCNO. 5136; OFB-3 Bacillus species which is preserved in the China microorganism bacterial strain preservation management committee common microorganism center (CGMCC), the preservation date is August 15, 2011, and the preservation number is CGMCC NO. 5137; (2) mixing the three strain oil removing bacteria according to the volume ratio of OFB-1: OFB-2: OFB-3 of 1:(0.9-1.1):(0.9-1.1), and the viable count of the three plant oil removing bacteria is 109-1011 per ml; (3) using the mixed bacteria liquid for fermentation amplification culture in the industrial culture medium, fermentation process condition is as follows: the fermentation temperature is 28-32 degrees C, the inoculating amount is 4-6 v/v, stirring speed is 100-200 rpm, fermentation time is 30-60 hours, in the process of fermenting the air to the culture medium per minute air to gas-liquid volume ratio of 1-1.5; (4) after the fermentation is finished, plate-and-frame press filter through a hydraulic ferment, pressing pressure is 0.2-0.6 MPa, the water content of is 40-50%; and (5) removing water by using boiling type drying tower, the moisture content is 8-10%, the drying temperature is 60-80 degrees C, drying and crushing, to obtain the dry powder. An INDEPENDENT CLAIM is a method of using the obtained oil removing agent for processing oil field sewage by air/oxygen (A/O) biological contact oxidation method, comprising: (1) in the biochemical pool to be filled with water, aerating the water until dissolved oxygen reaches 3-4 mg/L; (2) adding the water weight in the biochemical pool, the ester is 0.05-0.15% per gram of dry powder, the viable bacteria number is 109-1011; (3) adding in biochemical pool, the pool of water until chemical oxygen demand (COD) reaches 600-1000 mg/L, then the tank, adding 5-15 mg/L of corn powder, 10-30 mg/L of wheat bran, 370-630 mg/L of inorganic phosphate, and 750-1250 of inorganic ammonium salt, in the biochemical aeration pool, water dissolved oxygen is maintained at 1-3 mg/L to promote microbial growth to biological film on the padding; (4) bio-membrane, growth well and hanging the filler, oil-containing waste water cultured and naturalized; at the design speed of the feeding speed 10% the oil field oil-containing sewage, oil content in sewage is 5-20 mg/L, sulfide 2-20 mg/L biochemical system oil rate is more than 98%, sulfide removing rate reaches 100% after every day so as to increase the water speed of 10% continuously feeding the oil field oil-containing sewage until the designed feeding speed continuously feeding and oil field oil-containing sewage is 100%, the step of adding inorganic phosphate, inorganic ammonium salt, in the pool C:N:P of molar ratio of 100:(4.8-5.2):(0.9-1.1), dissolved oxygen is not less than 4 mg/L; and (5) after the 100% feeding speed, the actual continuous processing oil field oil-containing sewage, maintaining biochemical pool inlet oil is less than 100 mg/L, sulfide is less than 50 mg/L, at the same time, every day the tank, adding inorganic phosphate, inorganic ammonium salt, in the pool C:N:P is 100:(4.8 -5.2):(0.9-1.1), pool aeration treatment, dissolved oxygen is not less than 4 mg/L.