Abstract: Due to the layer-by-layer process, the mechanical performance of the additive-manufactured part is often different from that produced by traditionally manufactured process. In the field of the aerospace, nuclear and medicine, additive-manufactured parts are difficult to serve as the main load-bearing structure due to the lack of the study about the fatigue property, which limits the generalizability of additive manufacturing technology. Here, the simulation method is adopted to study the high cycle fatigue property of the additive-manufactured 316 steel. The research results show that the crack initiation at the slip bands and grain boundaries is the main cause of the high cycle fatigue for the additive-manufactured 316 steel. In this paper, a micromechanical model is proposed to study the high cycle fatigue property of AM 316 steel, where the mechanical responses of grains and grain boundaries are calculated by the phenomenological crystal plasticity theory and elastoplastic cohesive zone model, respectively. For fatigue assessment, Papadopoulos fatigue criterion and a shakedown-theory-based fatigue criterion are adopted to consider the effect of dislocation slips and grain boundaries on the fatigue property, respectively. Finally, in order to verify the validity of the proposed micromechanical model, the simulation results of AM and rolled 316 steel are compared. As same as the experimental results, the simulation results show that AM 316 steel has a better fatigue property compared with rolled one.