The invention relates to a prefabricated assembly type composite slab suspension supporting structure and a composite slab construction method thereof. The prefabricated assembly type composite slab suspension supporting structure is characterized in that the prefabricated assembly type composite slab suspension supporting structure comprises supporting vertical rods, supporting horizontal rods, supporting inclined rods, horizontal inclined rods and horizontal connecting rods, rod parts are connected with each other to form a supporting system through square plate ports and diagonal lug plates, and the supporting system is suspended and supported on a prefabricated beam through internal threaded steel pipe embedded parts embedded in the prefabricated beam side, beam side fixed screws and lug plates. The composite slab construction method includes the steps of ribbed concrete composite slab prefabrication, prefabricated beam installation, supporting unit assembly, supporting unit suspension, supporting system forming, supporting system preloading, ribbed concrete composite slab lifting, ribbed concrete composite slab perforated steel bar construction, upper-layer reinforcement binding, composite slab flat-fell seam processing, composite layer concrete casting, and supporting removal, the construction period can be shortened, the material loss and the engineering quantity are lowered, the engineering cost is lowered, and the prefabricated assembly type composite slab suspension supporting structure has good technical and economic benefits.