The invention discloses a cleaning agent of circulating water for washing recycled plastics, relating to the technical field of water treatment. The cleaning agent is composed of the following components in parts by weight: 100 parts of lucid ganoderma, 250 parts of tobacco, 100 parts of Chinese gall, 100 parts of melia azedarach, 100 parts of cypress, 100 parts of rhubarb or lime, 100 parts of garlic, 100 parts of rhizoma atractylodis, 100 parts of folium artemisiae argyim, 500 parts of honeysuckle, 500 parts of herba houttuyniae, 500 parts of cyrtomium fortunei, 500 parts of isatic roots, 100 parts of gardenia, 400 parts of scutellaria baicalensis, 100 parts of coptis chinensis, 250 parts of golden cypress, 300 parts of officinal magnolia barks, 500 parts of white paeony roots, 200 parts of clove, 100 parts of logwood, 80 parts of semen cassiae, 500 parts of galanga, 100 parts of pepper, 500 parts of astragalus, 500 parts of rhizoma curcumae, 500 parts of perilla leaves, 300 parts of radix saposhnikoviae, 250 parts of radix angelicae, 250 parts of asarum, 100 parts of cinnamon and 100 parts of anise. The cleaning agent is simple in component and low in preparation cost, the water purified by using the cleaning agent is good in quality and capable of realizing circular washing, and no wastewater is discharged; in addition, due to the adoption of the cleaning agent disclosed by the invention, the quality of the plastics can be improved, the silk yield can be increased, and the prepared modified plastics are nontoxic, pollution-free and incapable of generating any injury to human bodies.