The one-dimensional equivalent linear method for soil layer seismic response analysis is widely used in engineering practices and academic fields. LSSRLI-1 and SHAKE2 000 are typical codes.LSSRLI-1，which represents the 1980s skill level，is recommended in Chinese manuals on seismic safety evaluation practices.SHAKE2 000 represents a more internationally advanced level.Improvements to LSSRLI-1 must be made with respect to the drawbacks of the equivalent linear method it uses.To reveal the differences between LSSRLI-1 and SHAKE2000，we established a horizontal layered model for class-Ⅰ to class-Ⅳ sites.Then we ran the two programs on the same working cases.A comparison and statistical analysis of the results shows the difference between the two programs and we therefore propose a variation of the relative deviation rule.Results indicate that peak ground acceleration （PGA），the spectrum，and the shear strain results do not obviously coincide in class-Ⅲ and class-Ⅳ site conditions. But in class-Ⅰ and class-Ⅱ sites conditions，there is little difference between the results of the two programs.After preliminary analysis，we conclude that the shear strain calculation method can be improved by modifying the shear modulus method to narrow the gap between LSSRLI-1 and SHAKE2000 results.We make this conclusion on the basis of the relative relationships between the shear strain，the PGA，the spectrum，and the shear modulus relative deviation.