A maintenance interval optimization model for wind turbine gearbox considering the maximization component profit per unit time was presented in this paper. First, the principle and configuration of gearbox were introduced, and the failure characteristic is analyzed as well as the failure rate distribution of components in gearbox. Then, the concept of component income coefficient λ and element utilizing rate per unit time U(t) were given. λ describes the proportion that component takes up the total income of wind turbine electric power sale，and U(t) represents the average income per unit time to wind turbine electric power sale during 0~t. Based on above two concepts the model of optimizing maintenance interval was proposed. Last, the paper used the proposed method to evaluate wind turbine gearbox maintenance interval in an actual wind farm. The simulating results indicates that the component profits per unit time for gears, intermediate speed shaft bearings and high speed shaft bearings increases by 16.88%, 30.26% and 32.59% respectively.