Abstract: The noise of subsonic jets endangers the service life of aircrafts and affects the lives of residents near the airports. To further reveal the acoustic radiation mechanism of subsonic jets and predict the sound field, a new hybrid method is developed. In this paper, the evolution of an axisymmetric mode in subsonic jets (Ma = 0.9, Re = 3600) are investigated by a direct numerical simulation (DNS). The acoustic radiation is calculated based on the acoustic model proposed by Wu and compared with the direct numerical simulation. Results show that if the primary instability waves dominate the linear process, the sound source is almost non-compact. Conversely, when the nonlinear effect needs to be taken into account, the difference frequency and sub-difference frequency waves are dominant and the sound source is slightly compact. But the direction of sound radiation is nearly 30° with respect to the jet axis for both linear and nonlinear situations, which is consistent with previous results.