The present invention discloses a method for treating sludge of the sewage treatment plants by using circulating fluidized bed boiler combustion. The method includes the following steps: (1) Preparing step of sludge coal mixture by adding fine coal and dispersant into sludge from the sewage treatment plants, then stirring and adding stabilizing agent; (2) clean burning step of the sludge coal mixture by feeding the prepared sludge coal mixture into the circulating fluidized bed boiler for clean burning, wherein a furnace of the circulating fluidized bed boiler contains fluidized media of quartz sand and limestone. The preparation of the sludge coal mixture also includes the steps: firstly, waste water is adsorbed and filtered by fine coal and CaO to form the resulted coal sludge into which others fine coal is added, thus the sludge coal mixture is prepared.