The invention provides a connection device of a thin-wall flexible tube and a connection method thereof. The connection device includes a joint, a firm sleeve built in the joint and used for supporting the joint, and an outer ring sleeves the flexible tube so as to compress the flexible tube onto the joint. The connection device is characterized in that an outer wall surface of the joint is provided with in turn: a limiting baffle plate 1, a groove, two inner sides of a limiting baffle plate, and two or more pawls which are arranged. With the direction of the pawls, it is convenient for the flexible tube being inserted while not exiting. The outer ring is made from plastic material which expands and becomes flexible after water absorption. The inner wall of the outer ring is provided with two or more pawls with the direction opposite to that of the joint pawls. During a connection state, the position of the pawls is staggered with that of the joint pawls. The connection device is fully made of plastic. The sealing connection to the flexible tube and the joint is realized by using the character that the plastic outer ring material expands and becomes flexible after water absorption and elastically and naturally contracts, and the special size design that a gap of the outer ring and the joint is less than the wall thickness of the flexible tube.