The utility model discloses a prefabricated plate cast -in -place beam's inclined roof board structure, including the inclined roof board prefabricated plate, the prefabricated plate is one -way slab, and long limit direction is reserved and is had lap joint steel bars when prefabricated, and lap joint steel bars is parallel with the minor face direction, and the inclined roof board structure still includes cast -in -place beam, the inclined roof board prefabricated plate passes through the lap joint steel bars overlap joint on corresponding cast -in -place beam, through pouring cast -in -place beam's concrete will complete frame system of prefabricated plate and cast -in -place beam structural formation, the utility model discloses a prefabricated plate cast -in -place beam structural change the structure structure of traditional inclined roof board structure, combine its construction side method itself, when reducing the construction degree of difficulty and construction risk, also reduced corresponding construction period, the lap joint steel bars that reserves through the prefabricated plate in addition realizes prefabricated plate and cast -in -place beam's seamless overlap joint, forms the complete structure system of a whole connection.