Abstract: As one of the core parts of mini car's drive axle, the comprehensive performance of hub bearing has a great impact on the transmission efficiency of mini car's drive axle, consequently, optimizing its internal structure to improve the transmission efficiency has important practical significance to improve the fuel economy of the vehicle. In this paper, the main factors affecting the comprehensive performance of hub bearings are analyzed. Based on the structural characteristics of a mini car's drive axle, the influence rules of working clearance, seal form and grease performance of hub bearings on the transmission efficiency of drive axle are studied by making the drive axle prototype and testing the drive efficiency. Experimental results show that the working clearance, seal form and grease performance of hub bearings have a significant impact on the transmission efficiency of drive axle. Compared with the rear axle hub bearing with small working clearance, the evaluation value of drive axle's transmission efficiency can be increased by about 0.38% if the rear axle hub bearing with large working clearance is adopted; and the transmission efficiency of the rear axle can be increased by about 0.53% if the rear axle hub bearing with non-contact seal is selected instead of the contact seal; while when low resistance grease is adopted inside the hub bearings, the evaluation value of drive axle's transmission efficiency can be increased by about 0.46% compared with the use of conventional grease.