The invention provides a method for preparing L-aspartic acid and L-alanine by using maleic anhydride. The method comprises the following steps: heating the maleic anhydride as the raw material to obtain a maleic acid solution through hydration reaction; adding maleate isomerase and L-aspartase; after filtering and concentrating obtained liquid of enzymatic reaction to deaminize, regulating the pH value until the isoelectric point of the L-aspartic acid is equal to 2.8 by using the maleic acid solution as an acidifying agent; crystallizing to separate out the L-aspartic acid; and converting the L-aspartic acid into the L-alanine by further using aspartate decarboxylase. The L-aspartic acid is prepared through one-step reaction by a two-enzyme method, the process is simple and convenient, the conversion ratio is high, production of malic acid as a by-product can be controlled effectively, and the quality of the product is good; and maleic acid is used as the acidifying agent to prepare the L-aspartic acid in an isoelectric point crystallization manner, crystallization mother liquor can be used as an enzyme reaction substrate and then is recycled, the discharge amount of waste water is greatly reduced, and the method conforms to the idea of environmental protection. In addition, the L-aspartic acid is further converted into the L-alanine by an enzymic method, so that products obtained by a whole process are diversified; and the market competitiveness is high.