In view of welding process,joint condition,crack shape,and facility structure,analyzes the causes for cracking of weld joints of connecting pipes from low-temperature superheater to pendant superheater at a power plant in operation. The results show that weld joints are exposed to stress concentration with coarse HAZ grains while various stresses overlap to create peak stress within the sensitive temperature of reheat cracking. Thus,the peak stress leads to loosening stress and results in cracking. To avoid such problems,a few effective repair procedures and preventive countermeasures are proposed,providing reference for enterprises to prevent and control similar problems.