A miniature underwater shock wave pressure sensor based on optical fiber Fizeau cavity is described. The basic theory and fabrication process of this sensor are given. This transient interference phase of the Fizeau cavity acted by shock pressure wave is demodulated by using passive homodyne demodulation technique. A static calibration test and a dynamic calibration test are conducted using a piston-type pressure calibration machine and a focusing-type electro-magnetic shock wave source. The results indicate that the linearity, repeatability, hysteresis, and intrinsic error of the sensor within the full pressure range of 0-60 MPa are 3.26%, 0.01153%, 0.07%, and 3.407%, respectively. The dynamic response time is less than 0.75 μs.