Abstract: Based on both the coupled nonlinear Schrödinger equations,the nonlinear propagation of two femtosecond laser pulses in the different regimes of photonic crystal fibers was solved by solving the equation group with the slip-step Fourier method.The effect of the pump pulse power,pump frequency chirp and various pulse widths on signal pulse compression was discussed in detail.The numerical results show that the signal pulse can be compressed through cross-phase modulation and the optimum fiber length can be obtained.It is also found that the compression factor increases with initial positive chirp and power, however,the optimum fiber length decreases.In order to obtain larger compression factor,pump pulses with narrow pulse-width are desirable selected.These results offer theoretical references for weak signal pulse compression by using photonic crystal fibers.