The large thick wall equipment tube（52 mm at the thinnest part of the plate） was affected by constraints and environment during the construction process,and the traditional technology method and Fangfashigong caused cracks in the weld seam. In this paper,we describe the cracks in three stages of welding,bottom beating and post-welding heat treatment during the construction of large thick wall equipment,analyze the environmental factors,construction technology and Shigongfangfa,and formulate effective improvement measures. The method of increasing the density of positioning welding,the thickness of positioning welding,the slow cooling after welding,and adjusting the process control of the number of segmental heat treatment are used to avoid the crack defects again. It can avoid the crack defects in the subsequent welding activities of the equipment cylinder,and it can provide effective experience for the subsequent assembly activities of the similar thick wall equipment,and ensure the smooth completion of the welding energy and quality of the large thick wall weld group in the relevant fields.