Abstract: Aiming at the frequent operation of supplementary steam valves in peak load regulation of thermal power units under high proportion of new energy grid connection, a dynamic coupling model of heat and electricity is established to reveal the impact mechanism of supplementary steam valve operation on the stability of electrical equipment. Based on a 600MW supercritical unit test platform, the dynamic characteristics of voltage fluctuation, harmonic distortion and stability margin under different supplementary steam valve openings and load change rates are quantitatively analyzed. The research results provide theoretical basis and engineering guidance for the coordinated control of heat and electricity in thermal power units under wide load peak load regulation conditions.