Based on analysis of the basic soil mechanics properties of natural argillaceous siltstone which are located in different sections of the construction site,the method of adding lime or cement to improve the soil is raised. Furthermore,we can define the difference of lime and cement mixed in soil through unconfined compressive strength and CBR test,which will help to determine the way to improve the subgrade by mixed with cement. Finally,we observe the changes in the strength of cement soil under the dry-wet cycle test,which simulate the process of cement soil under the environment of frequently alternate dry-wet on site. And the reliability of improving argillaceous siltstone by cement is confirmed ultimately.