The treatment effect and mechanism of municipal solid waste incineration bottom ash aggregate (BAA) on soils were investigated. The strength and deformation of BAA treated silty clay, BAA treated mucky soil were conducted by CBR test, unconfined compressive strength test, and resilient modulus test, respectively. The influence of BAA proportions, curing period, water saturated treatment, drying wetting cycle treatment on the strength and deformation property of BAA treated soils were investigated. Then, the chemical composition and mineral composition of BAA were investigated by XRD test, therefore the treatment mechanism of BAA treated soils were analyzed subsequently. Results show that CBR value, resilient modulus and water stability of two treated soils increase with the increase of BAA proportion and curing period. The property improvement effect of BAA on silty clay is better than mucky soil. The friction effect, hydraulicity, and pozzolanic reaction of BAA are the main reasons for the property improvement of soils. Considering test results comprehensively, it is recommended to treat soils with highly active BAA, and BAA proportion and curing period should be increased appropriately.