Three-dimensional nonlinear finite element analysis on long-short piles composite foundation is finished by using the Drucker-Prager yield criterion and ANSYS procedure. The influences of length and modulus of long and short pile on long-short piles composite foundation loading characteristics are analysed through research on nine long piles and sixteen short piles. The results are given as follows. The composite foundation settlement decreases linearly with the length of long pile increases. The composite foundation settlement has hardly decreased with the length of short pile increases. These conclusions are of referential value for engineering.