The formation processes of fuel spray of Stirling engine under different back pressure were investigated by using high-speed camera. And the influence of several parameters, such as back pressure in the combustion chamber, the flow-rate as well as the diameter of spiral channel, on the spray performance was analyzed. Results showed that: back pressure has great impact on the formation process of fuel spray; the fuel penetration and spray angle increase with the increase of fuel flow rate; the penetration increases and the spray angle decreases as the back pressure in the combustion chamber increases; at the same flow rate, with the increase of diameter of spiral channel, the penetration increases while the spray angle decreases.