Using wetting balance method, the wettability of Co73Si10B17 in amorphous and crystalline states by Sn and Sn-based lead-free solders (pure Sn, Sn-0.7Cu, Sn-0.3Ag-0.7Cu) were studied in the temperature range of 290-310. The surface state and wettability of different systems were represented by measuring the surface energy and wetting force. The results show that oxide films exist in Co-based alloys surface because its surface free energy is less than the intrinsic value. The wettability of the Sn-based solder is enhanced with increasing the Sn content. Thus, the wetting mechanism is a series of complex multiple reactions of removing oxide film and it is exceedingly strong. The final wettability of Co73Si10B17 is affected by the interfacial reaction product and surface oxide film, but it is determined by the degree of removal of the oxide film. © 2020, Science Press. All right reserved.