Active control techniques are crucial for enhancing the decay of wing-tip vortices. However, the complex instability mechanisms of wing-tip vortices hinder the optimization of control strategies and the understanding of their effects. This study investigates the instability evolution of wing-tip vortices under the influence of synthetic jet (SJ) actuators with various SJ frequencies by Stereoscopic Particle Image Velocimetry (SPIV) and Proper Orthogonal Decomposition (POD). Experimental results show that a frequency of 5 Hz most effectively promotes vortex dissipation, with significant reductions in peak tangential velocity (approximately 25%) and enhanced vortex wandering characteristics within the SJ frequency of 0–60 Hz. Additionaly, vertical vortex wandering is more pronounced than horizontal wandering, as evidenced by greater fluctuation amplitudes. Analysis of the first- and second-order modal evolution reveals their critical roles in promoting vortex instability and structural fragmentation, respectively. These results highlight the potential of active control strategies, particularly at resonant frequencies, to accelerate vortex dissipation.