Abstract: A modified Johnson-Cook model was proposed based on the true stress-strain data of 316LN stainless steel and it was successfully used to describe the deformation characteristic of the steel at room temperature and low strain rate. By making use of the finite element software ANSYS/LS-DYNA, a numerical simulation of cold roll-forming was performed for AP1000 primary pipes. The influence laws of forming parameters on wall-thickness reduction, such as wall-thickness, relative bending radius and friction, were investigated. An empirical formula of wall-thickness reduction for AP1000 primary pipes was proposed by the numerical simulation method. Furthermore, a full-scale cold-bending experiment of AP1000 primary coolant pipes was carried out for verification, and it indicates that the simulated result is accurate and reliable.