A kind of vector optical fiber hydrophone based on the composite structure of variable cylinder and diaphragm is designed. Firstly,the theoretical model of the hydrophone′s sensing principle and vector building principle is analyzed,the mathematical expression of hydrophone′s phase-shift sensitivity is obtained and the sensor′s design parameters are discussed. Then the probe head of hydrophone is manufactured according to design parameters. Experiments on the sensor′s sensitivity-frequency curve and the “8” glyph directional diagram are carried out in the first class underwater acoustic measurement station of the national defence. This hydrophone′s sensitivity reaches the value -155 dB re rad/μPa(800 Hz),and the experimental result agrees well with the theoretical value. Some errors are mainly caused by that the theoretical model is not accurate enough,and there is also some resonance in the test equipment and the fixing bracket.