The invention relates to the technical field of environmental pollution control, in particular to a chemical membrane coating agent with a surface heavy metal chelating curing function, and a preparation method thereof. The chemical membrane coating agent is prepared from the following substances in percentage by mass: 20 to 40 percent of functional ingredient A, 15 to 35 percent of functional ingredient B, 2 to 4 percent of auxiliary ingredients and the balance of water, wherein the functional ingredient A is formed by reaction liquid after the reaction of one or a combination of several from sludge protein liquid, percolate concentrated liquid or polyethylene glycol emulsion, a heavy metal chelating agent and formaldehyde or polyformaldehyde; the functional ingredient B is prepared from one or a combination of several from polyacrylic acid emulsion, vinyl acetate emulsion or modified PVC (polyvinyl chloride) emulsion; the auxiliary ingredients consist of a penetrating agent and a defoaming agent. The prepared chemical membrane coating agent has the advantages that during the application, little foam is generated; a coated membrane has high compactness, high anti-permeability, proper hardness, proper flexibility and adhesive force; the coating strength of the formed membrane is high; the combination performance of the membrane and an ash sample is good; the stability is high; a good isolation effect is achieved on flying ash; meanwhile, a chelating curing effect can be achieved on heavy metal of surface flying ash; secondary pollution caused by heavy metal leaching is prevented.