Single-mode laser Lorenz system is a typical nonlinear model, which shows extremely complex and richdynamic behaviors. It is very important to the research on characteristics. Based on a brief introduction of single-mode laser Lorenz system, which including model establishment, dynamic equations and relative system characteristics, theprogram is programmed by Matlab software and the phase maps of single-mode laser Lorenz system with different pa.rameters is simulated by a computer. With simulated images, dynamic behaviors of the system are analyzed and dis.cussed. The results show that when the parameter of the system is more than the value of a branch point, the system be.comes unstable and thus enters into a chaotic state.