In order to develop a better understanding of the controlling mechanism of fuel atomization, an investigation was carried out to evaluate orifice flow pattern and its effect on fuel atomization. Experiments were performed under atmospheric conditions on scaled−up model nozzles and metal nozzles with different orifice entrance configuration and nozzle L/D ratio. The orifice flow pattern and the jet appearance were observed by photographic technique and the Sauter mean diameter was measured by light scattering technique. It was found that the orifice flow, which usually exhibits two characteristic patterns, the flow with contraction and reattachment, and the flow free from the wall, will lead to distinct jet appearances near the nozzle exit. For a certain injection velocity at the nozzle exit, the pattern with flow contraction and reattachment will yield smaller droplet size than the pattern with flow free from the wall. The orifice flow pattern and the injection velocity at the nozzle exit are two predominant factors in the fuel atomization.