Abstract: In this paper, X70 pipeline steel was taken as the research object. High temperature tensile tests were carried out at different temperatures and strain rates. Damage model parameters such as the threshold strain, critical damage strain and critical damage were obtained, and damage evolution equations based on BONARO model was established. The damage evolution process of in-service welding was simulated and compared with the experimental results of in-service welding. The influence rules of medium pressure and wall thickness on the damage evolution behavior of in-service welding were studied. It was found that: during the in-service welding process, molten pool below the maximum damage value of the inner wall is located in the largest fusion deep behind the 1mm to 2 mm area, damage value in thickness direction decreases from the fusion line to the inner wall; decreasing inner medium pressure and increasing the wall thickness can reduce the damage at the bottom of molten pool, thus reduce the risk of burn through.