The invention discloses an agar compound colloid being dissoluble at low temperature and high in gelling strength and a preparation method thereof, and belongs to the technical field of food processing. The agar compound colloid is obtained through the steps that compound agar and auxiliary materials are extruded by a twin-screw extruder, dried and crushed, wherein the compound agar comprises Indonesia agar and gracilaria asparagus agar, the mass ratio of the Indonesia agar to the gracilaria asparagus agar is 1:2, and one or more of corn starch, microcrystalline cellulose, beta-cyclodextrin and carrageenan are adopted as the auxiliary materials. Meanwhile, the invention provides the preparation method of the agar compound colloid. The agar compound colloid has the advantages of being low in dissolving temperature and high in gelling strength; the agar compound colloid can be dissolved at 50 DEG C, and the gelling strength of the dissolved agar at 50 DEG C can reach 625 g.