Based on the advantages of digital image correlation method in the characterization of local mechanical property for welding joint, the differences in mechanical property, hardness, and microstructure of as-received, tempered, and solution treatment and aging (STA)-treated welding joints of 15CrMoR base metal with Ni-based welding material were compared. The tempering treatment transforms the dendritic structure into the dispersed tempered sorbite in the welding fusion zone (WFZ). The uniformity of mechanical properties is improved, and the matching degree of mechanical property between base metal zone (BMZ) and WFZ is improved. STA treatment transforms the dendritic structure into the uniform columnar dendrite structure in WFZ, which causes the disappearance of pearlite and the grain coarsening in BMZ, resulting in the degradation of strength and the increase of mismatching degree between WFZ and BMZ. Therefore, the suitable heat treatment needs to balance the requirements of BMZ and WFZ to obtain the excellent comprehensive mechanical property for welding joints.