Pressurized water reactor (PWR) pipeline is an important part of a nuclear power plant, and the temperature and pressure of pipelines are the key parameters reflecting its health status. It is closely related to the service life and production safety of nuclear power equipment. Therefore, the distributed temperature–pressure dynamic monitoring technology of PWR pipeline has become the research focus in this field. Traditional electrical sensors cannot withstand high temperature, high-pressure water vapor environment, and pressure multiparameter networking measurement requirements. Therefore, this paper proposes a distributed temperature–pressure dynamic monitoring method for PWR pipelines based on the fusion of fiber-optic FP cavity temperature–pressure composite sensor and distributed FBG temperature sensor. Through optical fiber metallization and laser welding technology, the problems of sensor packaging and curved surface following installation under high-temperature environment are solved. At the same time, this paper proposes a hybrid demodulation theoretical model of Fabry–Perot (FP) and fiber Bragg grating (FBG) sensing, and builds a distributed temperatures-pressure dynamic monitoring system for PWR pipelines by using Labview software. Finally, the temperature and pressure test experiments in the PWR pipeline were completed and the temperature and pressure sensitivities of the constructed FP thermo-pressure composite sensor were 0.264 nm/°C and 6.28 nm/MPa. This paper also completes the temperature–pressure monitoring at different measuring points during the cooling process of the pipeline, which verifies the feasibility and effectiveness of the proposed method. It is of great significance to the safe and stable operation of nuclear power plant system.