Abstract: The main girder is one of the important components ef cranes.The girders,ususlly weighing from 5 tons to 500 tons with their length ranging from meters to decame-ters,are manufactured by welding with A3,C3 and 16Mn steel plates.The main problem in manufacturing is the welding deformation.This thesis discusses,in addition to deformation calculation,the general factors affecting the welding deformation of the main gnder Practical centred measures are preposed to meet the tecnical require-ments.