Abstract: Reinforced thermoplastic pipes effectively address the problems of corrosion, scaling, low laying efficiency, and high comprehensive use cost of traditional steel pipelines. However, there is currently no standard to specify the winding angle of the reinforcement layer for non-adhesive polyester industrial filament reinforced thermoplastic pipes. To provide theoretical support for the production of adhesive type composite pipes, it is necessary to clarify the optimal winding angle for non-adhesive polyester industrial filament-reinforced flexible composite pipes. In this study, a mechanical theoretical model of reinforcement thermoplastic pipes under internal pressure was established. The winding angle of DN50-25 MPa reinforced thermoplastic pipes was determined and verified through experiments. The results showed that the actual radial strain of DN50-25 MPa reinforced thermoplastic pipes was twice the circumferential strain at 53.5°. The theoretical results were consistent with the experimental results, providing a critical theoretical basis for the production of adhesive polyester industrial filament reinforced thermoplastic pipes and holding significant practical application value.