The invention relates to an access hole locking device for a municipal water supply and drainage system, relates to the technical field of municipal facilities, and solves the problem that the whole municipal water supply and drainage system will be paralyzed as people can open a well lid of a pump well at random and once non-staff enters into the pump well to damage a water pump because existingpump well is covered directly by the well lid and the well lid is by no means locked. The access hole locking device comprises a locking assembly and a deadlocking assembly. The locking assembly comprises supporting blocks, a locking column, a connecting rod and a driving column, wherein the supporting blocks are uniformly arranged on the side, close to a well body, of the well lid circumferentially; the locking column penetrates the supporting blocks, is slidably connected to the supporting blocks and is inserted onto the well body; one end of the connecting rod is movably connected to the locking column; and the driving column is arranged on the well lid in a penetrating manner and is arranged concentric to the well lid, and on end of the driving column is movably connected to the end, far away from the locking column, of the connecting rod. The access hole locking device has the effect of improving the safety of the water pump in the pump well and guaranteeing normal operation of the municipal water supply and drainage system by locking the well lid, wherein the non-staff cannot enter into the pump well.