Abstract: In order to study the damage of the thermal power unit to the equipment during the peaking operation, the finite element software was used to analyze the stress change of a steam pipe under the peaking operation condition, and the safety status of the equipment was evaluated based on the fatigue life data of the material. The results show that when only considering the internal pressure stress, the inner wall stress of the steam pipe was about 40 MPa, and the outer wall stress was about 27 MPa. After considering the thermal expansion, the stress of the inner and outer walls of the steam pipe at the same position reached 98. 73 MPa and 62. 159 MPa respectively. The stress of the steam pipe was greatly affected by the thermal expansion stress of the structure, but the stress fluctuation was reduced. Thermal expansion stress had a great influence on the fatigue life of steam pipe.