NOVELTY - A solid acid catalyzed biodiesel oil is prepared by drying heteropoly acid at 40 degrees C for 24 hours, adding into round bottom bottle installed with soybean oil, adding methanol, avoiding water vapor in the air after condensation, oil bath magnetic force stirring, cooling, and evaporating using rotary evaporimeter to obtain mixed liquid; and transferring into pear shape dividing liquid funnel, adding saturated salt water, shaking, standing and delaminating to obtain upper layer biodiesel oil layer and lower layer saturated salt water layer, separating, and extracting.    USE - Method for preparing solid acid catalyzed biodiesel oil.    ADVANTAGE - The method solves parameter problem, and accords with state standard.    DETAILED DESCRIPTION - A solid acid catalyzed biodiesel oil is prepared by:    (A) drying heteropoly acid at 40 degrees C for 24 hours, adding into round bottom bottle installed with soybean oil, adding methanol, avoiding water vapor in the air after condensation, oil bath magnetic force stirring at 65 degrees C for 48 hours, cooling to room temperature, and evaporating using rotary evaporimeter at 40 degrees C to obtain mixed liquid;    (B) transferring into pear shape dividing liquid funnel, adding saturated salt water, shaking, standing an delaminating to obtain upper layer biodiesel oil layer and lower layer saturated salt water layer, separating lower layer saturated salt water layer, placing upper layer biodiesel oil layer into flat bottle, and extracting separated lower layer saturated salt water with ethyl acetate for 3 times; and    (C) placing into bottle installed with biological diesel oil layer, washing saturated salt water, standing and delaminating, washing saturated salt water, standing and delaminating, separating to obtain upper layer organic phase, adding into anhydrous sodium sulfate, drying for 2 hours, filtering, taking filter liquor, and evaporating using rotary evaporimeter to 40 degrees C.    The ratio of dried heteropoly acid and soybean oil is 1 mmol:40 g. The mass volume of soybean oil and methanol is 1 g:6.25 mL. The ratio of saturated salt water and methanol is 1:0.83. The volume ratio of ethyl acetate and methanol is 1:1.67. The mass ratio of soybean oil and anhydrous sodium sulfate is 1:1.25-1.875. The volume ratio of saturated salt water and methanol is 1:1.67-2.5.