The invention provides an environment-friendly flocculating agent, and a preparation method and application purpose thereof. Through being metered in percentage by weight, the environment-friendly flocculating agent is prepared from 10 to 30 percent of modified medical stone, 5 to 10 percent of hectorite and the balance water, wherein the modified medical stone consists of medical stone and chitosan quaternary ammonium salt grafted on the medical stone through chemical bonds. The flocculating agent has the advantages that any harmful ingredients are not added, so that the environment-friendly effect is achieved; the formula is simplified; meanwhile, the flocculating effect is further improved, so that the COD (chemical oxygen demand) removal rate is improved; the flocculating speed is accelerated; the paint slag agglomeration is large; the paint slag water content is low; the degerming, bacteriostasis and deodorization effects are achieved.