Abstract: Based on the chemical composition of 25Cr2Ni4MoV steel, three metal flux-cored wires with different nickel mass fractions (15%,19%,23%) were designed, and then the 25Cr2Ni4MoV steel plate was welded by metal active gas shielded arc welding. The effect of Ni content in the flux-cored wire on the microstructure and mechanical properties of the joint was studied. The results show that the weld microstructures of the joints were all composed of lath martensite, bainite and a small amount of acicular ferrite. With the increase of Ni content in the flux-cored wire, the lath martensite structure in the weld was refined first and then coarsened; the elongation and impact absorption energy of the joint increased, and the strength increased first and then decreased. When the mass fraction of Ni in the flux-cored wire was 19%, the tensile strength of the joint reached the highest value of 920 MPa, and the impact absorption energy was 48 J; the joint had good matching of strength and toughness.