In order to test the high applicability of HS990 Piston Aero-Engine, use different carburetors experiments on HS990 engine in an altitude simulation test cell. Test results demonstrated that the maximum operating height of HS990 piston engine exceeds 7km. An auxiliary electric fuel feeding assembly should be employed while the engine operating with a non-pressurized fuel tank above 5km. When the altitude is above 5km and the inlet temperature is below -18℃, the existing diaphragm carburetor will reduce or even stop fuel supplying, which finally caused the engine flameout. Comparing with the imported carburetor, HS990 piston engine adopting homemade carburetor has a better power- altitude performance, but less operating stability in high altitude. Appropriate cooling air flow will advantage the cylinder to decrease its operating temperature at high altitude. But excessive cooling air flow will cause the engine operating instability due to the lower temperature of cylinder.