By using finite difference software FLAC3D, the displacement field and stress field of the long-short-pile composite foundation were studied, as well as the distribution of axial force, neutral position and penetration amount. The effects of the main parameters of long-short-pile composite foundation on its working properties, such as the modulus and thickness of the cushion, the length and quantity of the long pile, are investigated in detail. The results show that the modulus and thickness of cushion have less effect on the foundation settlement, while they can affect the pile-soil stress ratio significantly. Moreover, increasing the number of piles can control the foundation settlement effectively. The stresses in upper soil layer can be transferred to lower soil layer effectively, with the increasing of the number of long piles. Then the foundation settlement can be reduced correspondingly. While the variation of the number of piles has less effect on the stress field when the number of piles reaches a certain extend, and the reduction of the foundation settlement tends to slow down. Further, the foundation settlement decreases with the increasing of long-pile length. Finally, based on the foundation settlement control, the recommended values of parameters are given.