Abstract: The variations of spray characteristics （mean diameter and drop size distribution parameter） along radial distance and slant direction downstream of a pressure swirl atomizer have been measured. The corresponding analytical model has been proposed and the predictions of these variations have been made. The predictions agree very well with experimental data.It is shown that the Sauter Mean Diameter and drop size distribution parameter always increase with radial distance, but change very little along slant direction. The results show that it is very important to make the alignment of the laser beam to be in the same plane as the injection center line is, while it is not essential to adjust the laser beam to be perpendicular to the injection center line. The agreement between the experimental data and the predictions by the proposed model verifies the applicability of the model. Certainly it can be used to predict more complicated spray situation with some extensions.