Noise reduction and infrared (IR) signature reduction are the two main benefits from aero-engine exhaust plumes mixing enhancement. The mixing enhancement of a high temperature (800 K) and high speed (Mj = 0.9) axisymmetric plume subjected to a pair of piston synthetic jets (PSJ) with the mode number of 1 is investigated by using dynamic mesh model based RANS numerical methods. The numerical validations are conducted on the cases of Crittenden & Glezer's free PSJ [1] flows and Briges & Wernet's free jet flows [2]. The flow pattern of the actuated jet is investigated and the physical mechanism of PSJ actuated jet mixing enhancement is analyzed. Meanwhile, the impact of the exit diameter, and the frequency of PSJ actuator and injection angle to the mixing are investigated and the results indicate that all the factors play an important role on jet mixing enhancement in the selected conditions.