To research the influence of injection structure on gas-curtain generated by underwater launched gun, the three-dimensional unsteady mathematical model of multi gas jets in liquid tube was established, and the distribution of phase, pressure and velocity were numerical acquired. Numerical result indicates that after the injection of multi gas jets, Taylor cavities are formed in the liquid Tube. With the mixing process between the Taylor cavities and liquid medium, the multi gas jets merges and the gas-curtain is generated. During the merging process, the pressure in the flow field fluctuates and low-velocity vortex areas are formed on the gas-liquid interface. When the diameter of the slant nozzles increases from 1.5 mm to 2 mm, the reflux of the oblique jets is enhanced, which can result in the improvement of axial expansion performance of the side jets, and the drainage performance of gas-curtain is strengthened, the velocity of the liquid above the gas-curtain increases from 8.26 m·s^-1 to 9.4 m·s^-1 at 8 ms.