Abstract: The collaborative regulation of cementite and matrix in the microstructure of GCr15 bearing steel is a key technology to ensure the long-life, high-quality and stable service performance of bearings. The pre-treatment process is critical for controlling the morphology and distribution of the final carbides. In this paper, the synergistic evolution of the matrix microstructure and carbides in GCr15 steel under two pre-treatment processes,namely isothermal spheroidizing annealing (SA) and high temperature solid solution+isothermal quenching+high temperature tempering (HQT),were investigated. The results show that the SA-treated speciments exhibit distortion-free equiaxed ferrite grains and uniformly distributed carbides with high sphericity, while the microstructure of HQT-treated specimens consists of acicular martensite, fine bainite, and rod-like carbides.Although the carbide volume fraction is similar for both processes, the equivalent particle size of carbides in HQT is only about 1/4 of that in SA. Meamwhile, the densities of low-angle and high-angle grain boundaries, geometrically necessary dislocation density, and microhardness of HQT-treated specimens are much higher than those of the SA-treated specimens. Furthermore, the precipitation characteristics of carbides and elemental enrichment in carbides with different morphologies under HQT process are analyzed. This work provides a fundamental theoretical support for the precise control of heat treatment processes of GCr15 bearing steel and the development and manufacture of high-performance bearing products.