Aiming at exhaust pipe cracking failure of a single cylinder diesel engine, thermo-mechanical coupling approach based on equivalent vibration and material temperature effect was presented, and then varied stress was simulated using Finite Element Method. According to the modified Miner law and linear cumulative damage theory, considering stress gradient, surface roughness and temperature, dangerous position of exhaust pipe structure is predicted. The results show that exhaust pipe cracking is due to lack of stiffness in upper and lower direction. There is a risk of thermal modal resonance, and insufficient safety factor causes failure. Fatigue safety factor of original and support improved is 1.06 and 1.6, respectively. The predicted results agree well with measurements.