The strength of ship structure will be compromised due to thermal stress introduced by unbalanced temperature. This paper gives a brief research on the thermal analysis technology. Based on heat balance method, the thermal analysis was carried out for a MR tanker. Harmonized Common Structural Rules(HCSR) load combined with thermal load from 0 to 80 Celsius, the yielding and buckling strength of a web frame was then investigated. Results showed that, the thermal load will result in relatively large deformation to hull structure and also large local stress in bilge area . Even for cases of less than 80℃, thermal load in design stage should be properly considered. The approach used here is easy for use, the findings are of much engineering importance.