The invention relates to a biological drying method for activated sludge in sewage treatment plants in cities and towns. The method comprises a sludge pretreatment technology and a sludge aerobic fermentation-biological drying process control technology, wherein the sludge pretreatment technology includes the step of fully mixing the sludge with a moisture content and a conditioner in a mixing machine according to a certain ratio, and the sludge aerobic fermentation-biological drying process control technology includes processes of sludge degradation by microbial populations in a sludge top-layer fermentation bin, middle-layer fermentation bin and bottom-layer fermentation bin as well as the temperature change, mixture temperature and air inlet amount linkage automatic adjustment process control and exhaust amount process control in each layer, and material unloading from an upper-layer fermentation material bin to a next-layer fermentation material bin.