WC-17Co cermet coatings were deposited on Ni718 alloys using the high-velocity oxygen fuel (HVOF) technique. These coatings were then heat treated by different processes (150?°C, 10?h; 300?°C,?10?h; 450?°C,?10?h). The effects of heat treatment on microhardness, elasticity modulus, and fracture toughness were studied by an indentation method. The residual stresses of the coated specimens were evaluated by the Almen strip method. The results show that the phase constitution and the structure of the WC-17Co coatings exhibit no obvious change in 150, 300, and 450 °C heat-treatment. The microhardness, elasticity modulus, and fracture toughness of the WC-17Co coatings decrease with the increase of heat treatment temperature. The descent tendency of the mechanical properties is attributed to the decline in compressive residual stresses after isothermal heat treatment.