Based on characteristics which are unstable in essence, nonlinear and parameters uncertain of magnetic levitation system and chattering problems that exist in the conventional sliding mode control theory, this paper establishes a nonlinear and dynamics system model, using saturation function in place of switch function and designs a quasi sliding mode controller of magnetic levitation system based on combined reaching law. It demonstrates the system stability by using Lyapunov stability theory. From the simulation results, it can be proven that quasi sliding mode controller could effectively reduce chattering, with satisfactory static and dynamic performance and strong robustness.