Abstract: The different initial droplet size distributions are studied for their performance on the prediction of diesel spray structures under conventional injection pressures of 100, 200 MPa and ultra-high injection pressure of 300 MPa. The Blob method and the Rosin-Rammler distribution, which are commonly used to calculate the initial droplet size distribution in Eulerian-Lagrangian spray simulation, are compared based on the open-source platform OpenFOAM. The results show that at ultra-high injection pressure of 300 MPa, the spray penetration evolution is rather insensitive to the Blob method and the Rosin-Rammler distribution with a initial mean droplet diameter which is equivalent to the nozzle effective diameter, while is slightly reduced by reducing the initial mean droplet diameter. Although the initial droplet size distribution has a great influence on the sauter mean diameter(SMD), the effect decreases with the increase of injection pressure. A large number of droplets with diameter less than 1 μm will be produced at ultra-high injection pressure, and the initial droplet size distribution has a significant influence on the calculation of the formation process of droplets within this size range.