Abstract: Based on the tribological principle and the theory of contact mechanics, it is feasible to adopt curvature changing structure in the Rock bit journal bearing system. The structure and coupling relationship of curvature changing journal bearing under the condition without friction have been analyzed and three kinds of sub form structure configurations, namely, the pseudo curvature changing structure, the conformable curvature changing structure, and the clearance curvature changing structure, been differentiated according to the contacting features. The shape optimization and pre running in regulations of the contact surface of curvature changing journal bearing under friction condition have been established. The results of Rock bit journal bearing test indicate that the tribological behavior of the bearing can be effectively improved by curvature change based on both designing and pre running in.