Five-axis turning-milling center is an important and advanced NC machine in fields of military industry, aerospace, automobile and medical machinery. The model of machining center is established by using ADAMS and designing the variable parameters. The error of machining center is simulated by Monte Carlo method. The command file is compiled to simulate the machining center and the motion reliability is computed using simulation results. The whole process avoids establishing and solving complicated mathematical equations. So, it is an effective method for the analysis and computation of motion reliability. Compared with traditional methods, this method is more accurate and quick and it is suitable for complicated mechanism.