Numerical simulation model were established with FLAC3D to calculate the bearing capacity, the settlement of composite foundation with different lengths of pile and the stress of pile and soil. The lengths of pile entered in the hard soil which have influence on the bearing behavior of composite foundation have been analyzed. The results show that the length of cement-soil pile entered in the hard soil has no obvious influence on the bearing capacity and the settlement of composite foundation. The length of the pile entered in the hard soil should be taken from two to five times pile diameter.