The weak roadbed in sand soil area is a common problem in the highway construction. Adopting transient surface wave method combining with the test information of some drill holes, the relation model of the interface wave velocity and sandy soil the vertical and horizontal distribution characteristic mechanics parameters is built up in thip paper, and and regulation of the sandy soil mechanics parameters can be predicted in prospecting area. Through the practice checking, the predict result mainly coincides with the variety regulation of the actual sandy soil medium, which indicates that the mathematiced relation model built up in the paper is correcf and has higher practicability. The method will provide an economic viable way for prospecting and the classification evaluation of sandy soil in highway roadbed.