It is necessary to carry out shear design for in - situ hollow floor, which is concluded basing on the researches on “the code for design of concrete structures” , “technical specification for cast -in - situ concrete hollow floor structure” , experimental results and analysis of the structure of in - situ hollow floor, we should consider the difference between Cross rib and rib , and the importance of the stirrup . At last we provide the calculation formula of shear.