The elliptical orifice has potential benefits for improving spray and air fuel mixing quality, which have a great impact on combustion and emission performances for a diesel engine. This paper presents experimental and numerical studies on the internal flow and spray characteristics for an elliptical orifice with a large aspect ratio and circular orifice of diesel nozzles, under real diesel engine operation conditions. Large eddy simulation and Schnerr and Sauer models were adopted to study the cavitation flow, and the numerical models were validated first, regarding the mass flow rate and cavitation morphology. Two CCD cameras were adopted to acquire the macro elliptical spray images at the minor and major view planes, simultaneously. The results indicated that the discharge coefficient of the elliptical orifice was higher than that of the circular orifice, which indicated that the elliptical orifice has better flow performance as compared to the circular orifice. Also, the vapor volume fraction at the orifice exit for circular orifice was greater than that of the elliptical orifice, while the vorticity magnitudes were consistently lower than that of elliptical orifice under same injection conditions. Moreover, the cavitation distribution in the elliptical orifice in the direction of major axis shows longer length than that in the minor axis direction, and the cavitation morphology at the elliptical orifice exit showed a unique horseshoe shape, while the cavitation morphology for circular orifice was still distributing symmetrically. Furthermore, the spray width of the elliptical spray was greater than that of the circular one in all the view planes. Elliptical spray exhibited an axis-switching phenomenon during the injection process even at high injection pressure and back-pressure. Finally, the spray tip penetration of the circular orifice was always longer than that of the elliptical orifice; whereas, the spray cone angles of the circular orifice were much smaller than that of the elliptical orifice.