The concrete composite box steel girder floor system is a new box-section ribbed hollow floor system integrating the girder and plates by the″composite box″

one of the precast composite members and the afterward casting ribbed girder

which are divided into two types of open box and covered box according to in-situ layer on the top floor.The article researches its whole process under the effects of the fire and the service load.The results show that:（1）The failure form of the composite box steel girder floor system under the fire is that the composite box is burned and the floor loses its fire partition ability but it still has higher load carrying capacity and is able to withstand the loads acting on the floor system.（2）There is not burned because of the existence of concrete floor surface in-situ.（3）The bottom plate of the composite box is out of operation after burning and the floor structure becomes cross girder structure.（4）The deformation of floor is small in the fire.