In order to study the performance of gears under high speed and over load,the compound direct iteration method was used to simulate and analyze the lubrication state of high speed and heavy duty cylindrical gears in aero-engine transmission system.The effects of different power,different rotational speed and different lubricating oil inlet temperature on gear meshing zone pressure,oil film thickness and oil film temperature were studied.The results show that with the increase of gear transmission power or the decrease of rotational speed,the pressure in the meshing area increases and the oil film temperature increases.When the gear keeps a high speed,the power has little effect on the oil film thickness.Both rotational speed and power have an impact on the maximum temperature rise of the oil film,and power has a greater impact on the maximum temperature rise.At low power,the maximum temperature rise decreases first and then increases with the increase of rotational speed,while at high power,the maximum temperature rise decreases all the time with the increase of speed,and at fixed speed,the temperature rise increases with the increase of power.Under the condition of low speed and heavy duty,the oil film thickness is the thinnest and dry friction is easy to occur.The increase of inlet oil temperature will decrease the pressure,film thickness and temperature rise.Therefore,the appropriate lubricating oil inlet temperature can make the gear contact area bear lower load and have thicker oil film.