The spray characteristics of pressureswirl nozzle used in Stirling engine was studied by way of the experiment under high ambient pressures (up to 2.8MPa). The highspeed video imaging technique, FAM (Fraunhofer and Mie) laser drop size analyzer, and PIV (particle image velocimetry) test equipment were used for experimental measurements. Experimental results showed that the spray structure at higher ambient pressure was more compact. The vortex cloud was found at the leading edge at high ambient pressure. Spray cone angle was independent of ambient pressure after a value between 1.0~1.5MPa. The Sauter mean diameter (SMD) and the drop velocity became larger at high ambient pressure conditions. Finally, a vortex was found in the center of the spray and this region moved to the downstream of the spray as the ambient pressure increased.