Shaking table test is an important method to study seismic performance of geotechnical structures. Processing the similarity relation and deducing the response of original mold correctly are very important. Based on similarity theory, the paper adopts a dimensional analysis method to solve almost all similar constants, and provides a practical method on designing subgrade model of shaking table test. During the model designing process, several basic similar constants are defined at first and other main similar constants are obtained according to the basic similar constants. This method is applied in practical earthquake simulated shaking table test. Partial results are compared with the theoretical calculation result. The experimental result which is in concordance to the theoretical calculation result can reflect the seismic response rules of subgrade correctly. So the practical designing method is feasible.