The feasibility of repairing nickel-based superalloy components by IN939 powder was verified and the microstructure and properties of the repaired zone were investigated in this study so as to provide support for the repair of gas turbine components. The laser cladding process of IN939 alloy was explored, and the laser additive repairing of trapezoidal groove in nickel-based alloy using IN939 was carried out. The microstructure and the phase composition of additively repaired zone were characterized. Furthermore, the effects of microstructure evolution during the repairing on the repaired zone properties were investigated by micro-hardness tests and tensile tests. The results showed that the repaired zone of IN939 was dense and had good morphology without significant defects like cracks, pores. There are the γ-austenite phase and the Laves phase in IN939 cladding layer. From the bottom of the layer to the top, the cooling rate of the cladding layer decreases leading to increase of the primary dendrite spacing, while the Laves phase increases at first and then decreases. The average horizontal tensile residual stress at the interface was 346 MPa. From the bottom of the repaired zone to the top, the microhardness increases at first and then decreases. The average microhardness of the repaired zone was higher than the substrate. The average yield strength of the repaired samples is 548 MPa, and the ultimate tensile strength is 959 MPa. The tensile failure occurred in the substrate, showing a good metallurgical bond between the IN939 alloy and the substrate. The IN939 repaired zone has high mechanical properties and bonding properties after laser additive repairing, verifying the feasibility of laser additive repairing with IN939 powder.