This paper analyzes whether strength or stiffness restricts the design of the main girder of traveling and gantry crane.Through the structural theoretical analysis and combined with the relevant calculated data and curves,the conclusion is that strength or stiffness restriction is mainly related with the stiffness requirements,span range of the crane and the ratio of height and width,i.e.,when the requirement on stiffness of main girder is strict in a normal span,or the ratio of height and width of the main girder section is small,the design will be restricted by the stiffness.But when the requirement on stiffness is released,or in the case of very little span or very large span or the ratio of height and width of the main girder section is large,the design will be restricted by the strength.The above analysis can provide reference for crane design and has some practical significance.