In order to sure the stability of the embankment and sub-grade, it is necessary to improve the weathered soft rock which is used as the filling of embankment. Research is carried out such as part in different proportion quick-lime or cement, with soft rock of different water contents being artificial to mix and stir evenly, go on compaction test, work the biggest dry density and optimum water content, then unconfined compression strengths of the samples at different proportions, different curing ages and different compactness were compared. The relationships between strengths and contents of quick lime, ages as well as compactness of improved soil were further analyzed based on improving mechanism of quick lime and cement. Thus the best modified way and the best content of quick lime or cement were assured, the aim is to provide reference to further study and engineering application.