Copper alloys for electrical connectors are important materials for current applications in 5G communications, new energy vehicles, etc. Cu-Ni-Si system alloys are widely used in this research context because of their excellent mechanical and electrical properties and good resistance to stress relaxation. Research on the mechanism of the effect of the thermal deformation regime on the microstructure of Cu-Ni-Si system alloys is lacking. Based on this background, the thermal deformation behavior of Cu-Ni-Si alloy ingots was investigated under deformation temperatures ranging from 600~950 ℃ and strain rates ranging from 0.01~10.00 s-1. The results show that hardening and softening alternately dominate the deformation process at high strain rates, and the flow stress curve shows "wave-shaped" changes. The thermal deformation constitutive equation and processing map of the alloy were established, and the optimum control range of thermal deformation process parameters for Cu-Ni-Si alloys with high solute content was obtained at a deformation temperature of 900 ℃ or above. Moreover, the softening mechanism of the hot deformation process of the alloy under different deformation conditions was investigated by analysing the microstructural evolution of the alloy. At 950 ℃, the low strain rate leads to discontinuous dynamic recrystallization with bowing out of nuclei at grain boundaries, whereas at higher strain rates, continuous dynamic recrystallization mainly occurs with the merging of dislocations rotating to form new large-angle grain boundaries.