There is increasing demand for a finer atomization of fuel spray in order to improve the engine performance and mileage, reduce exhaust emissions and then improve the transient response. In general, for an engine to comply with this demand, exhaust turbocharger and EGR are necessary especially electronic fuel injection system. As a key part of electronic fuel injection system, the performances of electronic gasoline injector improve the engine power outlet and fuel economy. In other words, electronic gasoline injector can achieve a wonderful dynamic response to improve the combustion process and reduce the exhaust emissions in engine. The aim of this paper is to define a CFD methodology for the simulation of gasoline injector. A two-step work procedure has been adopted. First, three-dimensional computational models of gasoline injector with two kinds of valve seat are created. Then, the simulations are conducted for different geometric parameters of nozzles with properly initialized. The results are used to analysis pressure distribution and the changes of average velocity in the nozzles.