In engineering, the inclined plane model is generally used to calculate the transmission efficiency of the ball screw pair, which cannot reflect the influence of load on the transmission efficiency, and there is lack of experiment verification. Therefore, it is necessary to study the transmission efficiency of the ball screw pair under different loads. Starting from the force analysis of the screw, considering the contact deformation, merging the structural parameters and the actual working conditions, proposes a transmission efficiency calculation model. In order to verify the effectiveness of the transmission efficiency calculation model, a transmission efficiency test bench for the screw pair was developed, and the transmission efficiency test of a 4010 type double-nut ball screw pair was carried out. The results show that: The calculated value of the transmission efficiency model and the measured value of the test both increase with the increase of the load, and finally tend to be stable. The transmission efficiency calculation model can more accurately calculate the efficiency value of the ball screw pair under different loads. Compared with currently used calculation formula for engineering type selection, the proposed model possesses stronger scientificalness. In actual engineering type selection design, the transmission efficiency calculation model can be used to effectively estimate the efficiency according to the load conditions.