The invention relates to a composite uncoupling agent for reducing excess sludge in a sewage treatment process by an activated sludge method, which comprises the following components: 3,3,4,5-tetrachloro salicylamide, soluble copper salt and an adsorbent, wherein the soluble copper salt is one of copper sulfate, copper chloride or copper acetate; the adsorbent is one of refined diatomite or zeolite powder or a mixture of the refined diatomite and the zeolite powder; the weight ratio of the 3,3,4,5-tetrachloro salicylamide to the soluble copper salt is 1:0.05-0.25; and the weight ratio of the total of the 3,3,4,5-tetrachloro salicylamide and the soluble copper to the adsorbent is 1:0.05-1.00. The composite uncoupling agent has obvious positive effect, particularly stronger sludge reductionperformance. If the same weight reduction rate of the sludge is achieved, the added TCS (tetrachloro salicylamide) can be reduced by 25 to 75 percent, and after the TCS is added into a system, the removing rate of the COD (chemical oxygen demand) is basically not influenced.