The present invention requests to protect an early calculation and correction method for crank shaft strength of an internal combustion engine, and belongs to the technical field of engine crank shaft strength control. A crank shaft is one of core parts of the internal combustion engine, and has to satisfy certain strength requirements. Current crank shaft strength checking is correlatively conducted after a crank shaft 3D model is completed in general, and at the moment, certain major dimensions of the crank shaft are determined. For certain strength problems led by these major dimensions, design modifications need to be performed, so that the optimization cost is extremely high. The method can calculate crank shaft strength by a numerical method in an early stage of crank shaft design after the major dimensions are determined, and optimize design schemes not meeting strength requirements in time, thereby avoiding the risk of later design modifications.