Substrates of 30CrMnSiA and 30CrMnSiNi2A high-strength steels were repaired by a multilayer laser-cladding process using 30CrMnSiA alloy powders. The microstructures and mechanical properties of the cladding layers, substrates, and heat-affected zones were analyzed. The cladding layers on both the 30CrMnSiA and 30CrMnSiNi2A substrates exhibited a mainly sorbite microstructure. As the number of cladding layers increased, the sorbite and martensite contents on the 30CrMnSiA substrate decreased and increased, respectively, and a mainly martensite microstructure was observed in the cap layer. In the heat-affected zone (HAZ) of the 30CrMnSiA substrate, the microstructure was mainly martensite and small amount of blocky ferrite, and the ferrite was identified as the unmelted phase of the original ferrite matrix. In contrast, as the number of cladding layers on the 30CrMnSiNi2A substrate increased, the martensite content gradually increased, but sorbite remained the dominant microstructure. In the heat-affected zone of the 30CrMnSiNi2A substrate, the microstructure was mainly sorbite and coarse-grained martensite. The mechanical properties of the high-strength steels were also analyzed. The microhardness values were larger in the cladding layer on the 30CrMnSiA substrate than those on the 30CrMnSiNi2A substrate, and the softening phenomenon of the heat-affected zone was more obvious on the 30CrMnSiNi2A substrate than that on the 30CrMnSiA substrate. The tensile strength of the cladded sample on 30CrMnSiA substrate was over 90% of the substrate, and the impact toughness and elongation of the cladded samples were better than those of the 30CrMnSiA substrate. On the 30CrMnSiNi2A substrate, the cladding improved the impact toughness but significantly reduced the tensile strength and elongation. The results confirmed the suitability of 30CrMnSiA powders for laser-cladding repair of 30CrMnSiA steel. However, when the powders were used to repair 30CrMnSiNi2A steel, the heat input of the multilayer laser-cladding must be lowered to reduce the width of heat-affected zone, the formation of coarse-grained martensite, and the matensite decomposition.