The present invention relates to the scientific field of animal feed and discloses a grass carp growth performance improving feed and a preparation method thereof. The grass carp growth performance improving feed includes sargassum beta-1,3-glucan. The sargassum beta-1,3- glucan accounts for 0.1wt% of the grass carp growth performance improving feed. The feed is puffed feed prepared by puffing processing treatment. The grass carp growth performance improving feed uses the puffing processing treatment and the sargassum beta-1,3-glucan is added at the same time, which can significantly improve the growth performance of the grass carps. Experiments show that the grass carp feeding feed can significantly improve the relative fatness of grass carps, and thus significantly improve the growth performance of grass carps.