The transmission efficiency of manual transmission and its effect factors are studied by using experimental method. A test bench of transmission efficiency is built,a testing sample is manufactured,and the transmission efficiency experiment is carried out. The test results show that when load torque remain constant,the transmission efficiency increases with the increasing of input speed,eventually reaches the maximum,then decreases gradually. Given the same input speed and load torque,the transmission efficiency is highest when its gearshift is switched to the fourth gear. When the input speed remain constant,the transmission efficiency increases with the increasing of load torque. When the viscosity-temperature characteristics of gear lubricant is improved by adopting multistage gear oil or synthetic gear oil,the comprehensive efficiency can be increased by 0. 62% and 0. 96% respectively. When open-type bearings are adopted to reduce the friction loss,the comprehensive efficiency can be increased by 0. 52%.