Abstract: The nonlinear Schrdinger equation is solved by slit-step Fourier numerical method. The variation of B integral in several propagation media in the ultra-short pulse laser system is numerically simulated and briefly analyzed. The results show that B integral increases with input intensity and gain coefficient increasing. The shape of the input pulse has some effect on B integral, and the B integral of picosecond chirp pulse is smaller than that of femtosecond Gaussian pulse. It is also found that proper group-velocity and high-order dispersions can reduce B integral for the selected calculation model. The approach can be reference resources to the design of the ultra-short pulse laser system.