Abstract: The spray characteristics of high pressure common rail diesel engine are directly relevant to the combustion process and emission performance. The rail pressure is one of the main factors that determine the spray characteristics. The spray characteristics under different rail pressure are simulated by using the CFD simulation model that will be identified by experimental results. The result of the spray velocity field simulation show that the higher the rail pressure the better the spray characteristics are and the earlier the maximum velocity appears. However, the maximum velocity decreases and retentivity of velocity becomes worse. The spray characteristics differ much from mixture characteristics, especially around the injection hole.