The work aims to study the microstructure and electrochemical corrosion behavior of FeCrNiMo laser cladding layer, so as to solve the problems of hydraulic support surface protection and repair. FeNiCrMo alloy layer was prepared on 27SiMn steel substrate by laser cladding, and the microstructure and electrochemical corrosion behavior of this layer were investigated by XRD, optical microscope, SEM, potentiodynamic polarization and electrochemical impedance spectroscopy. Under optimized processing parameters, the layer had a single-cladding thickness of over 2 mm, without obvious defects like pores, cracks. The cladding layer presented a cellular dendritic structure involving martensite in dendrite and intergranular Cr/Mo-rich ferrite, thus achieving a good balance of strengthening and toughening. The cladding layer exhibited obvious passivation behavior in both 3.5wt% NaCl and 0.5 mol/L H2SO4 solutions. The passive region had a width of 300 mV and 1310 mV, the corrosion potential was detected to be –140.2 mV and 2.3 mV, the corrosion current density was measured as 5.0×10–8 A/cm2 and 1.3×10–3 A/cm2, and the polarization resistance was calculated to be 3.5×105 ?.cm2 and 6261.4 ?.cm2, respectively. This cladding layer depicted excellent corrosion resistance that was superior to the substrate, although selective corrosion occurred in micro-area due to duplex phase structure. Therefore, the designed FeNiCrMo alloy and related laser cladding parameters satisfy the engineering demands for processing efficiency and performance and can be used for protecting and repairing hydraulic supports.