The FE model of the gear, established by finite element software ANSYS, and the dynamic model of gear-pair, established by multi-body dynamic software SIMPACK, were combined to simulate. The gear’s FE model was used to compute the stiffness of the teeth, which was taken to calculate the integration stiffness of the gear-pair and imported to the SIMPACK model of gear-pair. Without the gear-pair force element, the gear-pair SIMPACK model was built through moved Markers, function expressions and input functions, to realize the meshing behavior, with techniques of generalized resonance and demodulated resonance, the faults could be diagnosed. The results showed that the difference of meshing integration stiffness between ANSYS and SIMPACK calculation was 2.65 percent. The error between meshing-vibration model and Gear-pair force element was controlled under 10 percent. The type of faults could be located by the frequency and the security level could be measured by the amplitude to reach the purpose of faults’ diagnosis.