The invention provides a sewage treatment agent. The sewage treatment agent comprises the following materials in parts by weight: 8-12 parts of potassium permanganate, 5-9 parts of bleaching powder, 43-60 parts of a composite flocculant, 15-20 parts of activated carbon and 5-6 parts of a regulator, wherein the composite flocculant is a mixture of polyacrylamide and chitosan. Through a good integrating effect of amine cations formed by amino groups in a molecular chitosan monomer on transition metal, thick and fine ions in water are effectively flocculated into large flocs through electrostaticattraction and the large flocs are settled, so that the sewage treatment agent has very high COD, SS and heavy metal ion removing rates, and thus such the sewage treatment agent with good performanceis obtained.