The invention discloses an unpowered automatic anti-overflow device for a multilayer roof drainage system. The device comprises a spigot and socket pipe and an anti-overflow assembly arranged inside the spigot and socket pipe. The anti-overflow assembly comprises an annular rotating shaft ring fixed to the inner wall of the spigot and socket pipe, a rotating shaft sleeve arranged on one section of the rotating shaft ring in an embedded mode, driving blades and water resisting blades symmetrically installed on the two sides of the outer wall of the rotating shaft sleeve, and a rotating space bin which is located on the side face of the spigot and socket pipe and provides turnover space for the driving blades; the water resisting blades are sheets consistent with the spigot and socket pipe in cross section shape, when the rotating shaft sleeve rotates, the water resisting blades are turned over to be perpendicular to the axis of the spigot and socket pipe, and the spigot and socket pipe is blocked. According to the unpowered automatic anti-overflow device, the phenomenon that high roof rainwater overflows to a low roof through a pipeline system can be effectively avoided, so that the number of rainwater vertical pipes is decreased, the precious indoor space is saved, and the influence caused by the number of the rainwater vertical pipes on building internal and external ornament workloads is reduced.