A hinge device for mounting a toilet seat cover, which comprises: an upper base, wherein two ends of the upper base are respectively equipped with a mounting base (20,23); the inner sides of the mounting base are provided with a connector (9,13) respectively; the rear side of the upper base is equipped with multiple rotatable connectors (1,3,5,6) for mounting a toilet seat circle and a toilet seat cover; a lower base, wherein two ends of the lower base are respectively equipped with a fixing hole (8,12) matching said mounting base (20,23); the connectors (9,13) are inserted into the fixing holes, locking the lower base on a toilet the lower base is provided with chutes (26,28); the upper base is equipped with inserts (19,24) matching the chutes; the inserts and the chutes are matched with each other so that the upper base can be inserted into the lower base along the set direction; a locking pin which comprises a rotatable rod which is mounted on the lower base; the inner end of the rod extends to a limiting base on the lower side of the upper base; the inner end of the rod is provided with a limiting stopper and the rotation of the rod causes the limiting stopper to depart from or to lock into the limiting base, wherein the front end of the rod is provided with a stirring handle; characterized in that the limiting base includes two parallel baffles (32,36); the rod extends in between the two baffles; both of the baffles are provided with limiting slots; the limiting stopper is a cuboid of which a side wall is connected to the end of the rod and the rotation of the rod causes the cuboid to insert in or depart from the limiting slots. an upper base, wherein two ends of the upper base are respectively equipped with a mounting base (20,23); the inner sides of the mounting base are provided with a connector (9,13) respectively; the rear side of the upper base is equipped with multiple rotatable connectors (1,3,5,6) for mounting a toilet seat circle and a toilet seat cover; a lower base, wherein two ends of the lower base are respectively equipped with a fixing hole (8,12) matching said mounting base (20,23); the connectors (9,13) are inserted into the fixing holes, locking the lower base on a toilet the lower base is provided with chutes (26,28); the upper base is equipped with inserts (19,24) matching the chutes; the inserts and the chutes are matched with each other so that the upper base can be inserted into the lower base along the set direction; a locking pin which comprises a rotatable rod which is mounted on the lower base; the inner end of the rod extends to a limiting base on the lower side of the upper base; the inner end of the rod is provided with a limiting stopper and the rotation of the rod causes the limiting stopper to depart from or to lock into the limiting base, wherein the front end of the rod is provided with a stirring handle; characterized in that the limiting base includes two parallel baffles (32,36); the rod extends in between the two baffles; both of the baffles are provided with limiting slots; the limiting stopper is a cuboid of which a side wall is connected to the end of the rod and the rotation of the rod causes the cuboid to insert in or depart from the limiting slots.