The laser cladding Co–Cr–W coating has coarse dendritic and network carbides, which can lead to crack and exfoliation easily, limiting the application of Co–Cr–W coating. In this work, friction stir processing (FSP) was carried out on a laser cladding Co–Cr–W alloy coating to modify its microstructure. FSP transforms the laser clad coarse dendritic grains (grain size: 2–4 μm) into nanograins (grain size: 50–200 nm) and crushes the network carbides into nanoparticles dispersed in Co-base solution. The microstructure and thickness of plastic surface layer are controllable by the condition of FSP. Moreover, a WC
reinforced Co–Cr–W thin layer was formed because the WC particles of stir tool were squeezed into the Co–Cr–W coating surface layer. More interestingly, when the FSP rotary speed was 1500 rpm, an interlocking bonding between Co–Cr–W coating and steel substrate was formed, which was favorable for the connection with substrate. The surface nanocrystallization significantly strengthened the laser clad Co–Cr–W alloy after FSP.