In order to explore the oscillation characteristics of the inlet unstart induced by the low Mach number inflow, an unsteady simulation study of a specific integration of the forebody and the inlet was carried out. A comparison of the oscillation flow field and the aerodynamic force of the aircraft under different incoming Mach numbers were performed. The results show that a stable periodic oscillation appears when the inlet is unstart at the low Mach number. And the cycle length of the periodic oscillation increases with the increase of the incoming Mach number. Due to the throttling in the inlet throat, the oscillation flow field can be divided into two stages, which are the increasing and decreasing stages of the separation bubble in the throat. Meanwhile, the distribution trends of the mean and amplitude of the pressure along the tunnel both exhibit high at throat and low at both ends. And the increase of inflow Mach number will increase such trend. In the oscillation period, the variation trends of the lift coefficient CL and the drag coefficient CD are quite different, while the lift drag ratio curve is manifested as the trend of increasing with the throwing up of the separation bubble and decreasing with the swallowing of the separation bubble. CL and CD decrease with the increase of Mach number, but the amplitude of pulsation changes little, and the lift drag ratio is not sensitive to the change of Mach number. CL and CD both decrease with the increase of Mach number, but the amplitude of oscillation changes little. And the lift-drag ratio is not sensitive to the change of Mach number. In addition, in the process of self-starting, it is found that once the instantaneous flow in the throat is higher than that in the starting to a certain extent, the separation bubble at the throat can be swallowed completely. Because the swallowing process cannot be simulated by the steady simulation accurately, the self-starting Mach number obtained by the steady simulation is higher. © 2021, Editorial Department of Journal of Propulsion Technology. All right reserved.