The invention discloses an automatic air exhaust device used for a pressure container. The automatic air exhaust device comprises a valve seat and a floator arranged in the valve seat, wherein an airexhaust hole is formed in the top of the valve seat; a first C-shaped blocking ring is arranged on the bottom of the valve seat; the opening of the floator faces downwards; a step hole is formed in the upper end surface of the floator; skit holes which penetrate through inner and outer sides of the bottom periphery of the floator are formed in the bottom peripheral end surface of the floator; a guide slot which penetrates through upper and lower end surfaces of the floator is formed in the floator outer peripheral wall which corresponds to each skirt hole in position; a sealing ring is arranged in the step hole; a slot hole is formed in the upper end surface of the sealing ring; an O-shaped sealing ring is arranged in the slot hole; a C-shaped blocking ring slot is formed in the lower cylindrical surface of the sealing ring; and a second C-shaped blocking ring is mounted in the C-shaped blocking ring slot. The automatic air exhaust device is simple in structure, is easy in processing and manufacturing, is simple in mounting, is small in size, and does not need an electrical control system.