To study the influence regularity of the tail fin on the bubble flow pattern, the hydrodynamic characteristics of fins of supercavitation projectile were performed in water tunnel. The rationality of the test scheme was fully demonstrated. The test system of ventilation cavitation flow was constructed based on the high-speed water tunnel. Base on the basic shape of the projectile and the similarity theory, the tail force measurement test model was designed. Meanwhile, to change the relative location between the fins and the cavitation, the cavitation size or the model attitude was adjusted. The hydrodynamic characteristics of fins of supercavitation projectile were studied by changing the test conditions. The influence regularity of the tail fin on the bubble flow pattern and its hydrodynamic characteristics under different puncture conditions were obtained. The results show that the formation of secondary cavitation at the top and the side of the tail fin after the puncture of the tail significantly changed the shape of the main cavitation, and the impact of the tail fin on the main cavitation became more obvious with the increase of the puncture height. The hydrodynamic characteristics of the tail fin mainly came from the wetting part of the leading edge, and the lift coefficient and the drag coefficient increased significantly with the increase of the puncture height. The drag coefficient and the lift coefficient under puncture conditions increased linearly with the attack angle. The results can provide references for the optimization design of the shape of the supercavitation projectile and trajectory prediction.