This paper constructs a thermal energy storage and temperature regulation performance model for PCM in sportswear. An energy balance model of the human-clothing-environment system is established based on the first law of thermodynamics and coupled with the phase change kinetic equations, clarifying the influencing mechanisms of key parameters such as PCM content and exercise intensity. Polyester fiber fabric samples containing different PCM contents were prepared by coating and microencapsulation methods. Combined with environmental chamber experiments and COMSOL simulations, a three-factor, three-level orthogonal experiment was used to analyze the effects of exercise intensity, ambient temperature, and PCM application type. Results show that the novel nanodoped PCM coating (20\% content) achieves an energy storage density of 3860 J/m², a 23\% increase over conventional PCM. During moderate-intensity exercise, the internal temperature fluctuation (1.8°C) of the garment is reduced by 58.1% compared to the blank sample. During high intensity exercise at 400 W, the lowest temperature is 3.1°C higher than the blank sample. The error between simulation and experimental data is less than 5%, validating the reliability of the model and providing a basis for the optimized design of PCM sportswear.