A numerical simulation of transient temperature and stress field for a typical coke drum has been done in this paper by Abaqus secondary development. According to the result of simulation,a comparative analysis was done to explain the mechanism of circumferential and axial thermal stress. Under the considering of nested effect between coke and shell,the element node with a maximum Mises value was fond under a condition of proportional loading by the method of combined stress analysis.Based on the principle of the linear accumulation of fatigue damage,in order to calculate the theory life of the fillet weld connecting the skirt and conical head,the combined stress wave of the node before was divided into several whole cycles with Rain-Flow method. After that,when not considering of the nested effect,it is found that the circumferential stress would have a nearly 50 percent lower than the value calculated with nested effect considering. At last, a theoretical calculation of circumferential stress was carried on. It shows that the result given by FEA agrees reasonably well with the theoretical calculation value. Obviously,the result given by FEA was credible.