Transmission efficiency is an important index to measure the transmission performance of ball screw. The current researches on transmission efficiency lack in-depth analysis of the friction and lubrication of the contact surface. There are few experimental studies and most of them are for a certain type of sample. To obtain a transmission efficiency model that is more in line with the actual situation and analyze the influencing factors of transmission efficiency, based on the load distribution theory, the bearing and motion of the ball screw are analyzed, which consider the process error. The theory of electohydrodynamic lubrication is also combined to obtain the ball screw in different working conditions. According to the friction coefficient change rule under the conditions, a new transmission efficiency model is achieved. Then, the influence factors of transmission efficiency are calculated and analyzed. The final design test verifies the transmission efficiency model and analyzes the influence of different axial load, speed, preload, and lubrication viscosity on the transmission efficiency. The test results show that the maximum relative error between the calculated value of the new model and the test value is 6. 42% , which evaluates the validity and rationality of the new model.