An air inflator includes a double-cylinder body having a first cylinder having its one end connected with a compressed air adapter for supplying a compressed air therein and having its another end connected with an air filling applicator adapted to connect with a tire valve for filling compressed air into the tire, and a second cylinder fluidically communicated with the first cylinder and mounted with a pressure gauge thereon. The first cylinder is formed with an actuating rod reciprocatively moved in the first cylinder for controlling the air flow for filling a tire, or for sensing a pressure gauge for measuring air pressure, or for releasing excess air upon the adjustable depression of a handle pivotedly mounted on the body.