The plastic region at the notch root under multiaxial loading and its effect on fatigue life of 316L stainless steel notched specimens manufactured by selective laser melting are studied by means of fatigue tests and finite element analysis. The fatigue tests of 316L stainless steel notched specimens that are additively manufactured are carried out under uniaxial， proportional and 90° non-proportional loading paths. The effects of notch geometry， stress amplitude and loading path on the plastic region at the notch root are studied. Based on this， the characterization methods of plastic regions at the notch root are proposed. The fatigue damage parameters are constructed by using the maximum von Mises stress at the notch root and the proposed plastic region influence factor f. Finally， the multiaxial fatigue lives of notched specimens are estimated by the proposed method in conjunction with the uniaxial S-N curve of smooth specimens. The results demonstrate that the majority of the estimated lives by using the proposed method fall within the three-time scatter band.