Abstract: 40CrNiMoA high-strength steel plates were repaired by laser melting deposition. The microstructure, micro-hardness and corrosion resistance of the 40CrNiMoA high-strength steel substrate and repaired zone were studied by optical microscopy, scanning electron microscopy, micro-hardness testing and corrosion testing. The results show that the wear and corrosion resistance of the 40CrNiMoA steel substrate were greatly improved after laser melting deposition repair with high Co-Ni secondary hardening alloy steel powders. The repaired zone is composed of carbon-supersaturated ferrite, lath retained austenite, M₃C cementite and M₂C carbides. The heat-affected zone in the 40CrNiMoA steel substrate is plate martensitic structure transformed from the original tempered sorbite.