The main role of hub bearing is to bear weight and provide accurate guidance for the rotation of the hub, which bears both axial load and radial load, and is a very important component. The traditional automobile wheel bearings are composed of two sets of tapered roller bearings or ball bearings. The installation, oiling, sealing and clearance adjustment of bearings are carried out on the automobile production line. This structure makes it difficult to assemble in the automobile production plant, high cost, poor reliability, and the car in the maintenance point maintenance, but also need to clean, oil and adjust the bearing. Hub bearing unit is developed on the basis of standard angular contact ball bearings and tapered roller bearings, it will be two sets of bearings as one, with good assembly performance, can be omitted clearance adjustment, light weight, compact structure, large load capacity, for sealing bearings can be loaded in advance grease, omit the external hub seal and free from maintenance and other advantages, has been widely used in cars, There is also a trend of gradual expansion of applications in heavy-duty vehicles.