To address the problems that traditional electromechanical and piezoelectric/piezoresistive sensors are susceptible to interference in extreme electromagnetic environments such as explosive shock waves, exhibit response lag, and have difficulty capturing the rising edge, this paper proposes and fabricates an all-silica Fizeau-cavity optical fiber miniature dynamic pressure sensor based on the Fabry-Pérot (F-P) interference principle. The sensor integrates the characteristics of high sensitivity, high frequency response, and high spatial resolution. Its sensing unit is formed by fusion splicing a 125 μm single-mode fiber, a silica capillary tube, and a coreless fiber. By length-limited grinding and 40% HF chemical etching, the thickness of the coreless-fiber pressure-sensitive diaphragm is precisely controlled to 2~3 μm, achieving an approximately ideal two-beam sinusoidal interference output. To enable high-precision inversion of transient pressure, a three-wavelength light source excitation scheme and a passive homodyne demodulation technique with arbitrary deterministic phase spacing are adopted to extract, in real time, the interferometric phase shift induced by cavity length variations under shock loading. In combination with three-channel voltage normalization and a phase-jump compensation algorithm, the influence of insertion-loss differences and quantization noise on measurement accuracy is effectively suppressed. Static calibration experiments show that the sensor operates within the elastic regime over the entire measurement range; within 0~60 MPa, the full-scale nonlinearity reaches 2.23%, the repeatability is better than 2%, and the hysteresis error is less than 0.1%. Shock-tube dynamic test results indicate that when the resonance frequency of the high-speed photodetector is set to 20 MHz and the response time is 8 ns, the dynamic response time of the sensor system is less than 50 ns, which allows for the accurate reconstruction of the shock-wave pressure-time waveform. With the merits of microscale sensing and high-frequency response, the sensor is suitable for transient pressure measurements under extreme conditions such as explosive impacts and intense laser-induced near-field plasma shocks, and it can maintain stable output under strong electromagnetic and high-shock conditions, thus exhibiting considerable engineering application value.