An automatic inflation pump including a housing, an air inlet, an air outlet provided in the housing, a manual rotary switch, a sealing device located at the air outlet, an air pump provided inside the housing and a motor for driving the air pump. The manual rotary switch is provided thereon with a dovetail groove which includes a deep groove and two shallow grooves located at both sides of the deep groove. The sealing device includes a driving stem and an air sealing plate for sealing the air outlet. One end of the driving stem is connected with the air sealing plate. A spring is provided on the driving stem. One end of the spring is fixed on a free end of the driving stem and the other end of the spring is supported at the air outlet.