Provided is an esterification method for preparing biodiesel using waste oils and fats. Under the normal pressure condition, the mixture of methanesulfonic acid, ethanesulfonic acid or chlorosulfonic acid and erosion restraint agents is used as a catalyst, the using amount of the catalyst is little, the catalyst can be repeatedly used, erosion on equipment is small, through a demister arranged on the top of a reaction kettle, the utilization rate of raw oil and the yield coefficient of coarse methyl ester are improved, heat generated in the reaction process is used for preheating fine methyl alcohol and waste oils and fats, heat is circularly used, energy loss is reduced, methyl alcohol which is not reacted is recovered, and production cost is lowered. The acid value of raw materials of the esterification method is wide (15-180mgKOH / g), the reaction time is short, energy loss is little, production cost is low, the yield coefficient of coarse methyl ester is high, high-acid-value flora and fauna waste oils and fats are esterified in one time to be lower than 1mgKOH / g in acid value, the next transesterification can be directly carried out to prepare biodiesel, and the method is suitable for producing biodiesel in an industrial mode.