The mechanical properties and deformation mechanism of a novel Ni-Co-based superalloys at room temperature (25 ℃) and medium temperature (650 ℃, 700 ℃ and 750 ℃) were studied using SEM, EBSD and TEM. The results show that the yield strength and elongation rate of the alloy were 1176 MPa and 22.5% respectively at room temperature, and the decreasing trend with temperature increase. At room temperature, the main deformation mechanism is that a large number of dislocations slip, and the partial dislocations shear the γ′ particles into isolated stacking faults. When the temperature reaches 650 ℃, it is observed that microtwins run through the secondary γ′ particles and γ matrix，but it is mainly deformed that continuous stacking faults shearing secondary γ′ particles and γ matrix. At 700℃-750℃, the secondary γ′ particles and the γ matrix are sheared simultaneously by continuous stacking faults and microtwins, and the length of stacking faults and thickness of microtwins increase with temperature. In the 650 ℃-750 ℃ range, the mechanism for shearing a γ′ particles once transitions from APB to isolated stacking faults. This study discusses the variation of deformation mechanism with temperature and the formation mechanism of microtwins and stacking fault under medium temperature conditions. An atom interchange diffusion model for SEFS formation of a/6 <112> partial dislocation shear γ′ particles is presented, which explains the formation process of microtwins and provides a reference for the further development of novel Ni-Co-based superalloys with high performance level.