Pneumatic air tube straight fittings are known as PU tube connectors, including a joint body and a docking tube. The joint body is equipped with an O-ring and a guide ring on the inner wall of the joint end, and the joint end is equipped with a flexible positioning card that locks inward, and there is a flexible pull button nested between the clamping part a of the flexible positioning card and the outer surface of the guide ring, and the inner contact surface of the flexible pull button is beveled or rounded. There is a snap-on tab on the outer wall of the joint of the docking tube. The advantages of this quick coupling are quick and easy installation, small installation space, pressure and shock resistance, superior sealing performance, and long service life.