Abstract: In the design of modern power station, steel structure and steel plate-concrete combined structure were usually used to form the main structure, which realized seismic resistance through mutual effect. The whole construction process of steel structure involved a lot of welding work. Cold cracking and lamellar tearing were found in welding of steel structure due to problems such as thick plates, complex joints and limited space. Causes of welding cracks were not only problems of welding process such as preheating, post heating and welding heat input control, but also problems of improper joint layout and groove design. In this study, causes of welding cracks were deeply analyzed, and specific countermeasures were taken to improve heating method, control welding heat input and optimize welded joint, so as to eliminate welding cracks. Experience accumulated in this study and improvement countermeasures proposed not only have direct guidance for welding of steel structure with complex thick plates in power station, but also have a certain reference for steel structure welding in other industries.