Stress corrosion cracking (SCC) is one of the main ageing mechanism in light water reactor (LWR). 316L austenitic stainless steel was adopted in nuclear industry for its relatively high corrosion resistance. The SCC of austenitic stainless steel may occur as it is subjected to both the tensile stress and the caustic medium, with regard to maintaining the structural integrity of components in nuclear power plant, an accurate prediction and efficient assessment of the component lifetime is significant and necessary. The stress corrosion crack propagation behavior of the 316L stainless steel elbow of nuclear power plant was investigated through a numerical simulation method. Firstly a finite element (FE) model was created for the stainless steel thick-walled elbow (the outer diameter is 355.6 mm, the inner diameter is 275.6 mm), with a semi-elliptical shaped 3D defect introduced at the internal surface of the elbow as the geometry of the crack, which was consistent with a practical crack, the crack opening displacement (δ_i) was determined by the calculations through the Dugdale model; subsequently, according to the FE calculation results, establish the fitting formula of the stress intensity factor (K) varying with the crack depth (a) and additional stress (P), and the fitting formula of the stress corrosion crack propagation rate (da/dt) for elbows under two types of cold work deformation was deduced through the combination with the experimental data, the crack propagation time was then calculated using a iterative method for cracks which evolved from different initial crack depth values to certain crack depth values. The calculation results provided effective reference criterion for the nuclear power plant safety assesment. This investigation demonstrated that, when the cold deformation extent of the elbow part is relatively small ( with the hardness of 230~245 HV) and it is under the ideal condition (no initial additional stress), it takes around 57 a for the stress corrosion crack to penetrate the elbow, when the initial additional stress was elevated to 200 MPa, the elbow failure time was shrinked to 1/5 (no stress release), 2/7 (half-stress release) and 3/7 (total stress release) of the former; keep the same initial additional stress (200 MPa) and increase the cold work deformation extent (the hardness was increased from 230~245 HV to 275~300 HV), the elbow failure time was shortened to 2/5 (no stress release), 3/8 (half-stress release) and 1/3 (total stress release) for the elbow part with higher cold deformation extent compared to the part with lower cold deformation extent, thus it was observed that both the decrease of the extent of stress relaxation and the increase of the extent of cold work deformation contributed to the reduction of the residual life of the nuclear power plant 316L stainless steel elbow.