Trap with can prevent flowing backward and water seal difficult dry

The utility model discloses a trap with can prevent flowing backward and water seal difficult dry, including trap casing and water seal structure, the water seal structure includes water seal overcoat, water seal endotheca, goes up floating cover and goes up floating cover, and water seal endotheca bottom is unsettled in the top of bottom, the water seal overcoat is installed on the bottom, the water seal endotheca inserts in the inner chamber of water seal overcoat, in the water seal, form vertical water course between the overcoat and go up port and lower port, it is the ring slice with lower floating cover to go up floating cover, the cover is established and is put in the water seal and can follow water seal endotheca outer wall, it covers in the last port of the one -way closed watercourse in water seal overcoat top to go up the floating cover activity, the corresponding position department of the lower port of the vertical water course of qieyu sets up the bearing structure between water seal overcoat a