Acoustic field properties of an axisymmetric supersonic jet at both low and moderate Reynolds numbers were studied using the linear parabolized stability equations (LPSE). The results showed that

the dominant noisegeneration mechanism was determined by the characteristics of unstable wave. When Reynolds number was low

the unstable wave frequency band was relatively narrow. Since the unstable region of the disturbance wave was long along stream wise direction

the acoustic radiation region was large; the sound source was decentralized; and the radiation angle was hard to be determined. For moderately large Reynolds number

the unstable wave had a large unstable frequency wave band; the short unstable region resulted in a narrow radiation region

concentrative sound source and strong radiation directivity; and the direction angle increased with the increase of Strouhal number. The normal velocity had a negligible effect on the acoustic field for low Reynolds number

while it had to be taken into account when Reynolds number was large.