Under high-speed operating conditions, the power losses of oil churning accounts for a large proportion of the total power loss, and studying the power loss of gear oil churning is of great significance for improving transmission efficiency.A computational model based on fluid dynamics was proposed,which can calculate the oil churning power loss of helical gear pairs.In this model,the oil churning loss of the helical gear pair can be calculated through dividing the helical gear into several small slices along the contact line.The churning power losses of a gear pair was divided into three parts,including the power loss due to oil drag on the periphery (circumference) of a gear, the power loss due to oil drag on the faces (sides) of a gear and the gear mesh pocketing power losses,and the influence of immersion depth, rotational speed, helical angle, tooth width and modulus on the churning power losses of a gear pair was analyzed. The results show that the churning power losses of a gear pair increases with the increase of immersion depth, rotational speed, spiral angle, tooth width and modulus.Among them,rotational speed, tooth width, and modulus have a greater impact on the oil churning power loss, while immersion depth and helix angle have a smaller impact on the oil churning power loss.The gear mesh pocketing power losses accounts for the largest proportion of the whole churning power losses of a gear pair.