In order to analyze the nonlinear dynamics behavior of the gear system, different fault parameters are considered and fault models including single to othimpact, single-tooth stiffness, single-tooth wear and full tooth wear are es tablished and analyzed with the chaos oscillator method. Then，the change rules of attractors in the system are discussed. Results show that the chaos oscillator method can differentiate the degree of faults to provide theory support for gear system. Finally, a new method for fault diagnosis of rotary mach ineries is suggested.