Sand liquefaction evaluation plays important role in seismic investigation and design of building. Based on the contrast between the most frequent methods in the evaluation of liquefaction, such as the method recommended in code for seismic design of building(GB50011-2001) and Seed method, a new method for evaluation liquefaction is deduced. The method possesses many preferred qualities, such as its accurate result, the reasonable and simple process of calculation and the close relation with engineering. Extensive application is advisable.