The present application relates to the technical field of architectural engineering. Disclosed are a slab joint leakage-proof structure of a prefabricated roof panel, a prefabricated roof panel and a prefabricated roof panel system. The slab joint leakage-proof structure comprises a first leakage-proof layer. The first leakage-proof layer comprises two flexible structures which abut against each other and are arranged at the joint of a main rib on the long side of the roof panel and a main rib on the long side of an adjacent roof panel. Either of the flexible structures comprises a main body portion sealably attached to the main rib, and at least one protruding portion which is fixedly disposed on the main body portion, protrudes and extends into the joint, and can tightly abut against the other flexible structure. The protruding portions of the two flexible structures can enclose an air cavity layer sealably isolated from the outside. The air pressure of the air cavity layer is higher than that of the outside for preventing liquid on the bottom end of the joint from permeating into the air cavity layer and entering a room. The slab joint leakage-proof structure has good waterproof performance. The flexible structures are sealably connected to the main ribs, and are not easy to fall off, and the problem that the waterproof performance is poor due to the fact that a mortar is easy to fall off in an existing waterproof mode of filling the mortar is solved.