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• A 5 DOFs nonlinear dynamics model of four-point contact ball bearing was proposed. • The dynamic contact feature of FCPBB with complex operating conditions were investigated. • The interaction between balls and raceway may changes from 2-point to 3-point contact with pure axial load. • The ball may experience 2-point contact, 3-point contact and 4-point contact in one revolution in case of combined loads. Four-contact-point ball bearing (FCPBB), with a special double half inner ring structure, presents dynamic multi-point contact characteristics in service. The dynamic contact feature, such as 2-point, 3-point or even 4-point contact phenomena between balls and bearing raceway, lead to completely different bearing friction, heat generation and wear rates. Considering the oil film traction effect, the traction and contact equations for ball and four raceways were proposed, and the changes of bearing dynamic contact feature with complex operating conditions, such as high speed-slight load, combined axial-radial load, were investigated. As bearing preload increases, the interaction between the ball and raceway gradually changes from 3-point to 2-point contact. In this process, the PV factor in outer sub-contact area first increases and then decreases, which is the key factor in bearing friction loss. In case of combined load, the ball may experience 2-point contact, 3-point contact and 4-point contact in one revolution. Besides, when two-point contact occurs, the main-contact area has the largest PV value; when four-point contact occurs, the sub-contact area has the largest PV value. [ABSTRACT FROM AUTHOR]