Abstract: A frequency modulation method and system for a thermal power unit coupled with molten salt energy storage are provided. The method includes: decomposing the power grid frequency modulation response demand by VMD algorithm to obtain residual components and a plurality of modal components; calculating adjacent aliasing degrees of all the modal components, and dividing a high frequency modal component group and a low frequency modal component group based on an adjacent aliasing degree minimum value; if the high frequency modal component group only includes one modal component, equally dividing the residual components and the plurality of modal components into a high frequency group and a low frequency group according to central frequencies, and performing a plurality of fusion methods on modal components in the high frequency group to obtain different fused components.