Abstract: The transformation superplasticity in welding CGHAZ(Coarse Grain Heat Affected Zone) of EH36MOD steel and its effect on fatigue life have been studied with thermal simulating method. Experimental results evidenced that (1)the transformation superplasticity phenomena do exist in the simulated CGHAZ by using restrained displacement;(2)the fatigue life of the CGHAZ is increased by 19% with increasing the superplasticity strain from 0% (no transformation superplasticity) to 1.0%;(3)in the case of 1.0 % strain,the M-A constituent is a striped-massive mixed morphology,but in the case of 0% strain,the M-A constituent is of single striped form;(4) of the above two cases,the former micro-region stress,which was caused by the slip resistance of ferrite matrix,is smaller than that of the latter during fatigue fracture process,the former fatigue life is longer than the latter.