The stiffly-expanded composite pile is a new type of composite pile formed by sinking rigid pile in cement soil mixing pile. In order to study its bearing characteristics in complex soft soil-sandy soil foundation, a numerical analysis model of rigid composite pile was established based on finite element software ABAQUS, with the effect of core pile length and diameter, soil-cement pile length, diameter and elastic modulus, as well as soil-cement and pre-stressed high-strength concrete(PHC) pile interface and soil-soil interface shear strength on the bearing performance was analyzed. The results show that the bearing capacity and economic advantages of the stiffened composite pile are obvious. The bearing capacity of composite pile increases with the increase of research parameters, but the improvement is limited by changing the research parameters beyond a certain range. With the increase of load, the slope of axial force distribution curve of composite pile increases, and the load proportion of PHC core pile is about 93.32% ~ 95.40%. When the load exceeds 4 000 kN, the axial force of soil-cement pile increases sharply within the depth range of 10 ~ 16 m, and the axial stress ratio of core pile/soil-cement pile changes significantly near the depth of about 10 m. The research outcomes could provide references for the engineering design and application of the stiffly-expanded composite piles.