For the strength issue of solidified sludges, cement is used as the solidification matrix material for the composite agent, and the material comparison strength tests are conducted to optimize the admixture of the composite agent. The strength tests are carried out on solidified sludges under different cement and bentonite additions to study the strength characteristics of solidified sludges. The results show that bentonite can be used as the preferred admixture, and its special ion exchange and agglomeration effect make bentonite composite cement have a better solidification effect on municipal sludges compared to clay and shale. The unconfined compressive strength of the solidified sewage soil generally increases with the increase of the cement and bentonite added. The experiment shows that the combination of cement and bentonite can effectively solidify municipal sludges and improve the strength characteristics. The strength prediction model for solidified soil based on the experimental data can accurately predict the unconfined compressive strength of solidified soil.