The utility model relates to an air collecting device based on a large stretching body builder. The air collecting device based on the large stretching body builder comprises an air cylinder, an air collecting valve and an air storage bottle. A retractable rod of the air cylinder is connected with a movement balancing weight block of the large stretching body builder. The tail end of the air cylinder is connected with a height adjusting bar installed at the top end of the large stretching body builder through connecting pieces. An air outlet of the air cylinder is connected with the air collecting valve installed at the air inlet end of the air storage bottle through an air pipe. The air collecting device based on the large stretching body builder has the advantages that the air collecting device based on the large stretching body builder is improved on the basis of original fitness equipment, people can collect air in the process of building bodies, and therefore a pneumatic piton type permanent magnet linear generator is matched to generate electricity. On the premise of guaranteeing the normal process of building the bodies for the people, wasted physical energy is converted into potential energy of the air to be converted to electric energy at last, and use ratio of energy sources is improved. The air collecting device based on the large stretching body builder has the advantages of being energy-saving, green, environment-friendly, simple in structure, and the like.