Through the retaining wall test in laboratory, the lateral earth pressure distribution and the decompression performance of EPS with different EPS elastic modulus and different EPS thickness were studied．The influence of compression value of EPS board on the lateral earth pressure on retaining wall was also analyzed by FLAC^3D numerical modeling．The research results show that the EPS board can effectively reduce the earth pressure behind the retaining wall; the smaller the elastic modulus of the EPS board, the larger the thickness, the larger the external load on the surface of the backfill wall, and the more obvious the decompression effect of the EPS board; After the EPS board thickness increases to a certain extent, the decompression effect of the EPS board will not increase significantly．In actual engineering applications, the EPS board thickness reaches 0.1 times the wall height to obtain the best decompression effect．