Nozzle is an important part of a sprinkler irrigation system. The energy loss of the inner flow of nozzle affects the quality of spraying in the whole sprinkler irrigation system.The twodimensional CFD model of the inner flow with the 3D software UG was built, and the numerical simulations of speed, pressure, turbulence kinetic energy and so on for the inner flow were carried out by CFD software Fluent which used the navierstokes and kepsilon equations. The results shows that the rotational flow of speed, the pressure drop and the mutation of turbulence kinetic energy are existed in the inner flow of the traditional impact drive sprinkler, and the energy loss is bigger. According the results of the simulation, the inner flow was optimized simply, and the energy loss is decreased obviously. It shows that used CFD can reveal the flow of the inner flow. It gives a littler reference to the optimization of the inner flow.