Abstract: Cracking of boiler water wall pipe occurred in a power plant. The causes of cracking in water wall pipes were analyzed using methods such as macroscopic observation, chemical composition analysis, metallographic examination and hardness testing. The results show that residual stress was generated during the welding of the circumferential weld seam at the joint of the water wall pipe, and there were welding defects in the material. Under high temperature and pressure environments, the defects gradually expanded into holes and caused erosion damage to other pipe walls, ultimately led to cracking of the water wall pipe.