Abstract: According to semi-classical theory for random laser, the Maxwell equations with the rate equations of electronic population can be solved by Finite difference time domain method (FDTD). The saturation effects of quasi-state modes in 1-dimension random lasers were numerically investigated based on this theory. The spatial and frequency distributions of different quasi-state modes were obtained. The results show that some properties of quasi-state modes, such as localization, will influence the saturation effects of the random laser system. By investigating these effects, the best quasi-state mode with low threshold and high saturation intensity can be achieved as a steady system output through one single frequency pump.