Taking the piston of turbocharged diesel engine as the research object, the FEA model of crank and connecting rod mechanism and cylinder assembly was built and the stress distribution of piston was calculated under thermal load，mechanical load and thermal and mechanical coupling load. Then the thermal and mechanical coupled stress field was used as fatigue load and the fatigue life of piston was computed according to nominal stress approach. The results show that the short life region was the upper part inside piston pin boss. In this area, the minimum cycle is 8.823×10⁷ or around 1 470.5 h.Accordingly, the structure of piston is reasonable and can meet the application requirements of diesel engine.