In engineering, the excessive slip of shear connectors will arouse the failure of the beams, and cracks in the brittle material element can increase the slip. In this paper, composite beam is composed of the brittle and ductile material elements and there are cracks in the brittle material element. Based on the relation between the slip strain and flexural rigidity, defining rigidity coefficient as there are cracks in the brittle material element, the total change in the slip strain at a given section due to cracking of the brittle material is obtained. The end slip that incorporates the effects of the brittle material cracking is calculated by integrating the slip strain. Letting the end slip equaled to the ultimate slip of shear connectors, the ultimate load formation of composite beam is gotten.