NOVELTY - Bio-base carbon solid acid catalyst and bio-diesel oil is prepared by selecting natural matters of saw dust, branch, fibrin, xylogen, rice hull, fruit shell, or straw stalk, and crushing until 0.3-10 mm granules; using low temperature carbonization at 300-500 degrees C for 1-20 hours; using oxygenation treatment for black brown solid at 200-350 degrees C for 0.5-1 hours; adding sulfuric acid at 120-250 degrees C for 1-10 hours, adding into water, and drying to obtain bio-surfactant carbon solid acid catalyst; and using catalysis esterification reaction at 70-120 degrees C for 1-7 hours to obtain bio-diesel oil.    USE - Method for preparing carbon solid acid catalyst and bio-diesel oil (claimed) for alkylation, hydrolyzation, and hydration.    ADVANTAGE - The method utilizes abundant and low cost raw materials; has pure nature reproducible matter; is simple, gentle and controllable reaction condition, high catalyst active performance, great stability, and easy to recycle; and environment-friendly catalyst, and no cauterization for devices.    DETAILED DESCRIPTION - Preparation of bio-base carbon solid acid catalyst and bio-diesel oil comprises:    (A) selecting natural matters of saw dust, branch, fibrin, xylogen, rice hull, fruit shell, or straw stalk, and crushing until 0.3-10 mm granules;    (B) using low temperature carbonization at 300-500 degrees C for 1-20 hours for biomass under the protection of nitrogen, and obtaining black brown solid;    (C) using oxygenation treatment for obtained carbonized black brown solid at 200-350 degrees C for 0.5-1 hours;    (D) adding sulfuric acid for sulfuration reaction with stirring at 120-250 degrees C for 1-10 hours, obtaining reacted mixture, adding into water while stirring and washing, filtering and drying to obtain bio-surfactant carbon solid acid catalyst with concentration of sample and sulfuric acid of 1:6-20;and    (E) producing bio-diesel oil by catalysis esterification reaction at 70-120 degrees C for 1-7 hours, of the free fatty acid or the waste oil fact and the short chain alcohol in the consecutive fine distillation and water segregating esterification reaction device, with mol proportion of alcohol oil of 4-10:1; and catalyst concentration of 4-10%.