Abstract: In order to analyze the output characteristics in single-pulse mode-locked fiber lasers with different net cavity dispersion, a numerical model based on the nonlinear Schr dinger equation is conducted to analyze the pulse evolution in the cavity by using the split-step Fourier method. According to the numerical simulation, the relationship between some parameters in fiber lasers and the net cavity dispersion is proven theoretically, and in the case that the net cavity dispersion is positive, the output pulse is compressed outside the cavity numerically and the compression ratio reaches up to ten times. Then the values of the required dispersion and the pulse width after compression are calculated. The results show that the maximum small-signal gain coefficient is proportional to the net cavity dispersion in general. And when the small-signal gain coefficient reaches the maximum value, the pulse width and the time-bandwidth product(TBP) increase gradually, and the 3dB bandwidth increases first and then decreases with the increase of the net cavity dispersion. The conclusion can provide reference for optimizing passively mode-locked fiber lasers.