The invention relates to a threaded joint for forming a telescopic flexible pipe fitting. The pipe fitting consists of a pipe fitting sleeve and an external-thread screw ring outside the pipe fitting sleeve. A locknut, a rubber sealing ring, a gasket, a snap ring and a snap ring groove are arranged outside a connected pipe which is inserted into the pipe fitting sleeve, wherein the locknut is provided with internal threads which are engaged with external threads, the rubber sealing ring and the gasket are arranged in an external expansion port of the pipe fitting sleeve, and the rear end of the connected pipe is provided with the snap ring and the snap ring groove. The rear end of the locknut is provided with a circular-ring-shaped sliding chute and an anti-pull-out internal lug boss. A reasonable matching gap between the snap ring and the circular-ring-shaped sliding chute is selected, so that the situation that the snap ring moves and is difficultly subjected to radial slippage when the connected pipe is subjected to expansion caused by heat and contraction caused by cold is guaranteed, and the trouble-free operation is realized. A rubber compression amount and a matching gap which are appropriate are selected so as to enable the telescopic flexivity to be greater than or equal to + / -2.2. Without increasing the cost, the inserted length can be increased, and the reliability can be improved. The pipe fitting sleeve is made of a thin-walled pipe, so that the one-piece casting is not required, the materials are saved, and the cost is low. The threaded joint is arranged outside the external expansion port and isolated from a medium, thereby being applicable to any pipeline for conveying any medium, e.g. stainless steel, carbon steel, ductile cast iron, plastics, glass fiber reinforced plastics, and the like. Furthermore, the threaded joint is universal to pipeline interfaces with the same pipe diameter.