The invention discloses an online swimming ring air leakage detection device and a detection method thereof, which relate to the technical field of swimming ring air leakage detection. Whether air leakage happens to the swinging ring is quickly judged through detecting whether the change of a sinking depth at a certain point on the swinging ring is in a specified set depth range. The device comprises a controller, a rack and a horizontal polished rod, wherein the rack is provided with a first cylinder; the horizontal polished rod is provided with a detection table driven by the first cylinder; a supporting rod is arranged on the detection table; an upper pressing plate driven by a second cylinder is arranged on the supporting rod; a third cylinder is arranged in a box cavity; two ends of a pull rope are respectively fixedly connected onto a telescopic rod of the third cylinder and a top end surface of a detection rod; and a control end of an ejecting mechanism, the control end of the first cylinder, the control end of the second cylinder and the control end of the third cylinder are connected with the controller respectively. The device also comprises a falling detection mechanism for detecting the falling height of the detection rod, and the falling detection mechanism is connected with the controller.