As a common foundation form, prestressed thin concrete (PTC) pipe pile composite foundation holds high practical value and excellent application prospect. In actual projects, the determination of the additional stress distribution of underlying stratum in composite foundation is the emphasis and difficulty. Hence, the study of the properties of stress dispersion of PTC pile composite foundation is of great significance. Three sets static load tests on composite foundations with different cushion thicknesses are designed and conducted in Tianjin soft soil area. Based on the static loading tests, the bearing characteristic of the PTC pile composite foundation are studied. The effect of cushion thickness on the bearing capacity is also studied. The numerical simulation method about PTC pile composite foundation is established and verified through the static loading tests. Through the numerical simulation method, the additional stress dispersion behavior of composite foundation in different geological conditions is studied and the scope of diffusion angles is determined. The influence of geological conditions, pile depth and the external load on the diffusion angles are indicated and the influence laws are carried out. The analysis results can be a good reference to the engineering practice.