The microstructural analysis was carried out for the triplex stainless steel weld metals with ferrite+austenite+martensite phases. The 13%Cr-7%Ni steels with varying the Ni content were used for investigation. The microstructure of the weld metals indicated a cellular structure with AF or FA solidification mode. X-ray diffraction analysis revealed that the amount of retained austenite increased with increasing Ni content in steels. The formation kinetic of retained austenite in the weld metal was analyzed by simulating the solidification segregation, desegregation during cooling and martensitic phase transformation. The calculated morphology and amount of retained austenite were consistent with the experimental ones. It followed that the formation of retained austenite in the triplex stainless steel weld metals could be predicted by numerical analysis.