Fiber optic sensors are increasingly used in the field of battery safety monitoring. Because of the difficulty measuring the tiny air pressure changes inside an energy storage battery, this study utilized a structural model of a fiber optic Fabry-Pérot (FP) cavity end-face coating. The relationships between the film thickness, effective radius, and cavity length were studied, and their mutual constraints and theoretical foundations were explored in depth. A miniaturized fiber optic micro-pressure sensor with high sensitivity and high accuracy was designed. This micro-pressure sensor had a sensitivity of -239.836 nm/MPa and linearity of 0.998. It showed good linearity and stability in a pressure range of 100 kPa. The sensor was compact, simple, and inexpensive to fabricate and had high sensitivity and excellent pressure response characteristics.