In this paper, the features and the stability of droplet transition during laser-MIG hybrid welding are analyzed, and a method for monitoring welding process stability based on SPE is proposed. Stable droplet trajectory and velocity can improve the uniformity of weld formation. When the welding is unstable, there is a disordered short-time logarithmic power spectrum, increasing SPE, and decreasing weld width and spreadability. The power spectrum of STFT and its SPE of arc area can effectively reflect the stability of the welding process. This method utilizes the arc light features and provides a new idea for monitoring the laser-MIG hybrid welding process.