Dynamics model of rotor-bearing-seal system are solved by numerical methods. Leakage and critical speed effect of three kinds of seal gaps, eight kinds of seal diameter, eight kinds of pressure, eight inlet loss coefficients and twenty-one kinds seal length are studied in this paper. Through the study of labyrinth seal structure effect on critical speed, it compared the effect if there is labyrinth seal force. The results show that the method can accurately calculate labyrinth seal leakage and rotor system critical speed by compare DYNLAB program and TASCFlow program. By the leakage influence regularity study, it gets that leakage will increase with seal gap, seal diameter and seal length, and it get that leakage will decrease with pressure and inlet loss coefficients. By critical speed influence regularity study, it will increase the critical speed when the rotor system has labyrinth seal force. Labyrinth seal length has largest effect on critical speed, and labyrinth seal gap has smaller effect on critical speed than seal diameter.