The rotating speed of the transmission provides critical information for the system dynamics, especially for the fault diagnosis at varying rotating speed. For the gear transmission with fixed transmission ratio, the rotating speed can be estimated through the gear meshing vibration because there is proportional relationship between the gear meshing frequency and the rotating speed. A speed estimation method based on time-frequency fusion of the gear meshing vibration is proposed in this paper. The rotating speed is estimated through the fusion of Wigner-Ville distribution and wavelet scalogram and then peak search of the fusion image. By comparing with traditional speed estimation method based on time-frequency distribution, the proposed method show higher precision and less sensitivity to noise. This speed estimation method is applied to the speed estimation based on the gear transmission and then the estimated speed evaluation is adopted for order analysis of fault bearing vibration, and the testing result shows that bearing fault order can be effectively obtained.