Abstract: The tensile experiments at elevated were carried out on Gleeble-1500D thermo-mechanical simulator for 316LN steel. The notched radius of specimens with the dimensions of Ø/10.0 mm × 121.5 mm were 0.5,1.0,2.0,4.0 mm and ∞(smooth specimen). The temperature was 950℃- 1200℃ and strain rate was 0.5 s^-1. The variation law of area reduction of specimens was obtained under different deformation conditions. The distribution of stress triaxiality in minimum cross section was obtained by numerical simulation when specimens were started to tension. The experiments were compared with numerical simulation results.Resultsshow that:the plasticity of 316LN steel at elevated temperature depends on not only stress triaxiality,but also grain size. If the difference of grain size is not obvious,the stress triaxiality plays a leading role. The smaller the stress triaxiality,the bigger the area reduction,and the better the plasticity. If the difference of grain size is obvious,the grain size plays a leading role. The smaller the stress triaxiality,the smaller the area reduction,and the lower the plasticity.