NOVELTY - A solid alkali catalyst preparing method involves heating a porous silicon oxide material, and naturally cooling the heated silicon oxide material to room temperature. The cooled silicon oxide material is sealed and stored. An alkaline component is dipped with the silicon oxide material in a compound solution and de-ionized water, and the solvent is evaporated to obtain a solid product. The obtained solid product is heated from room temperature to 150-160 degrees C, and the temperature of the solid product is made constant for 3-6 hours. The solid product is cooled to obtain a solid alkali catalyst.    USE - Method for preparing a solid alkali catalyst that is utilized to prepare biological diesel oil (claimed).    ADVANTAGE - The method enables preparing the solid alkali catalyst with better catalyzing effect in a simple manner. The catalyst can be easily separated from a reaction system after completion of an ester exchange reaction, and can be recycled such that environment pollution is reduced. The solid alkali catalyst can produce high yield of biological diesel oil to about 85.0 wt% using plant oil, animal oil, catering waste oil or hogwash as a raw material.    DETAILED DESCRIPTION - A solid alkali catalyst preparing method involves heating a porous silicon oxide material at 100-150 degrees C for 3-5 hours, and naturally cooling the heated porous silicon oxide material to room temperature in a dryer. The cooled porous silicon oxide material is sealed and stored, where the porous silicon oxide material is provided with a mesoporous structure having 2-5 nm hole and 10-30 nm hole, specific surface area of the porous silicon oxide material is 500-1500 m2/g, and pore volume of the porous silicon oxide material is 0.8-3.5 cm3/g. An alkaline component chosen from an alkali metal or alkaline earth metal oxide is dipped with the porous silicon oxide material in a compound solution containing nitrate, carbonate or acetate and de-ionized water, the solution is continuously stirred for 1-12 hours at temperature of 25 degrees c, and the solvent is evaporated to obtain a solid product. The obtained solid product is heated with speed of 510 degrees C/minute from room temperature to 150-160 degrees C under protection of nitrogen. The temperature of the solid product is made constant for 3-6 hours, and the solid product is cooled naturally under nitrogen atmosphere to obtain a solid alkali catalyst, where content of a compound containing the alkaline component in the solid alkali catalyst is 1.0-10.0 wt.%.