The invention discloses a decolouring deodorizing sewage treatment agent. The decolouring deodorizing sewage treatment agent is prepared from, by mass, 1.5 to 2.5 parts of polyacrylamide, 1 to 2 parts of a coagulant aid, 3 to 8 parts of potassium peroxodisulfate, 3 to 5 parts of bentonite, 10 to 20 parts of starch, 5 to 10 parts of solvent lignin, 5 to 10 parts of a sodium phosphate-sodium dihydrogen phosphate buffer system, 10 to 15 parts of nekal, 8 to 10 parts of polyepoxysuccinic acid, and 2 to 3 parts of aluminium polychlorid. The decolouring deodorizing sewage treatment agent is used for solving technical problems of the prior art that conventional flocculating agents are poor in effects, and secondary pollution is caused by reagent ingredients; the decolouring deodorizing sewage treatment agent is wide in pollutant treatment range, excellent in effect, and wide in raw material resource, is friendly to the environment, and is non-toxic; the structural design of the coagulant aid is special, and obvious effects on the aspects of algae killing, decolouring, deodorizing, and organic matter degradation are achieved.