The invention discloses a method for synthesizing porous micro-beads through acid dissolution of fine coal gasification slag. The method comprises the following steps: 1, taking a proper amount of thefine coal gasification slag, and adding water to prepare a fine coal gasification slag slurry with the solid content being 10-30 wt%; 2, fully stirring the slurry prepared in step 1, performing gravity cyclone separation, and collecting the obtained heavy separation product to obtain a silicon-rich composite slurry; 3, mixing a proper amount of an acid solution with the silicon-rich composite slurry to obtain a mixed slurry, and performing an acid dissolution reaction; and 4, carrying out solid-liquid separation, washing and drying on a material obtained after the acid dissolution reaction toobtain the synthesis product. The invention also discloses a composite porous material prepared through the method. The porous material is obtained through controlled dissolution under mild conditions by using the high activity of silicon aluminum calcium iron in the fine coal gasification slag. The material has the advantages of good physical and chemical adsorption performances, simple preparation process, low cost, realization of further preparation of a water purifier from dissolved metal ions, realization of the comprehensive utilization of all components in the fine coal gasification slag, and realization of changing wastes into valuables.