The invention discloses a sludge drying device for detecting the water quality. The sludge drying device comprises a device body, wherein the device body is provided with a base; a preheating chamberis arranged above the base; a fixed frame is arranged above the preheating chamber; supporting columns are arranged above the fixed frame; an evaporating dish is arranged at the tops of the supportingcolumns; a heater is arranged below the evaporating dish; an annular frame is arranged above the evaporating dish; the device body is provided with an air scoop and a pipeline; a water collecting tank is arranged on the right side of the preheating chamber; a putting groove is formed inside the preheating chamber; a preheating guide pipe is arranged on the outer side of the putting groove; and acooling tank is arranged on the left side of the preheating chamber. The sludge drying device disclosed by the invention is simple in structure and convenient to use; evaporative treatment of sludge can be effectively realized, water in the sludge is removed and a solid part is retained; in addition, the device body is provided with a preheating part; and heat generated by self evaporating operation of the device body is used for carrying out preheating operation, so that the working efficiency is effectively improved and a large amount of resources are saved.