The performance of rolling bearings is often reduced due to the additional wear introduced by sliding contact. Therefore, it is very vital to study the evolution of the sliding wear process of the bearing material friction pairs. The tribological performance of the two kinds of material pairs, including GCr15-GCr15/Si.sub.3N.sub.4-GCr15, was analysed under oil-lubricated conditions with a pin-on-disc rig. The results show that with high initial surface roughness, the friction coefficients of the two pairs decrease as the load and speed increase, while in the stable wear stage, Si.sub.3N.sub.4-GCr15 friction pairs show better tribological properties than those of GCr15-GCr15 friction pairs. For lacks of information-rich studies and techniques of worn surfaces topography, an in-suit 3D microscope is adopted to obtain the topographies of friction and wear surface during the wear tests. The results prove that 3D topography can clearly characterize the wear process. 3D topography shows identical trend with the surface roughness (R.sub.a, S.sub.a and S.sub.q) and the friction coefficients. Citing mixing parameter S.sub.dr explores its feasibility for characterizing worn surfaces. The results illustrate that there is a close relationship between S.sub.dr and 3D topography, which can reflect the friction transition of a surface from running into severe wear. A low surface roughness indicates a small S.sub.dr.