The paper takes a realistic coke drum as an example. A finite element analysis model using ANSYS is made, acquired with indirect coupling method, and circumferential thermal stress field of coke drum is calculated. Especially, the boundary conditions are based on the measured data of the realistic coke drum. Then circumferential thermal stress field of coke drum is calculated. The calculation results indicate that the circumferential temperature difference with the same height has little impact to stress of the drum and the circumferential temperature difference has the most important effect on coke drum skirt, so the impact to circumferential cracking of the skirt weld cannot be neglected.