To investigate the effect of the jet hole structure parameters and the flow field conditions on the drag reduction of the underwater jet， a biomimetic fish model is established with bonito fish as the biomimetic object. The jet model is established by adding a crescents jet hole to the side of the biomimetic fish model by simulating shark gills. The effects of air jet model and water jet model on drag reduction under different jet hole geometry parameters and different flow field conditions are analyzed by numerical simulation. In the range of conditions set in this paper， when the jet hole position X=20 mm， the aspect ratio k=2， the jet hole height h=15 mm， the velocity ratio is 0.5， and the mainstream field velocity is 10 m/s， the maximum drag reduction rate of the water jet model is obtained as 24.64 %， and the maximum drag reduction rate of the jet model is 10.17 %， which shows that the water jet model has a good drag reduction effect. In this paper， the effects of jet medium on the surface drag reduction of bionic fish is also analyzed by CFD simulation， which provides a basis for the design of new underwater vehicles.