Micropitting is a phenomenon that occurs in Hertzian type of rolling and sliding contact that operates in mixed elastohydrodynamic or boundary lubrication regimes. If micropitting does not arrest and continues to propagate, it can develop into macropitting and other modes of gear failure. For the high repair cost, gears for Large Megawatts Wind Turbines require high reliability, which should be studied in detail. The computation of local lubricant film thickness, local flash temperatures and safeties against micropitting of gears for large Megawatts wind turbines is carried out by ISO/TS 6336-22 and a calculation model based on the numerical thermal elastohydrodynamic lubrication (TEHL) contact theory with the consideration of the effect of pressure and temperature on viscosity is presented in this study. The oil film pressure distributions and film shapes are calculated at some varied contact points. Compared with results by ISO/TS 6336-22(ISO), the results show that there are some differences between the two methods in local flash temperatures and local lubricant film thickness, i.e. the maximum temperature rises and the minimum oil film thicknesses, but the quite consistent influence trends by each varies. The local lubricant film thickness calculated by TEHL contact theory is more sensitive to the load, and the thickness is higher, but the safety against micropitting is lower. The local lubricant film thickness is sensitive to the lubricant kinematic viscosity at 100 ℃ and the lubricant inlet temperature, but not sensitive to the lubricant kinematic viscosity at 40 ℃. The greater the kinematic viscosity, the thicker the local lubricant film thickness. However, since the permissible specific film thickness increased more, the higher the lubricant kinematic viscosity at 100 ℃, the smaller the safety factor against micropitting. The profile shift coefficient of gear has a great influence on the local lubricant film thickness, and the profile shift coefficient for the optimal special sliding or the minimum sliding velocity are not the maximum safety factor against micropitting, which should be considered in gear profile design. Long-term continuous operation with heavy load should be avoided and adequate lubricant with low inlet temperature should be provided, and the kinematic viscosity of lubricant, especially the kinematic viscosity at 100 ℃ should be regularly detected for wind turbine main gearboxes.