The invention discloses a dry anaerobic degritting and impurity removal system and a degritting and impurity removal method for a horizontal tank. The system comprises a tank body, wherein a pluralityof impurity removal channels are formed in the inner wall of the bottom of the tank body, an impurity removal header pipe is arranged below the tank body, each impurity removal channel is communicated with the impurity removal header pipe, and a rapid pipe joint connected with a vacuum pump is connected at an outlet of the impurity removal header pipe. The impurity removal channels and the impurity removal header pipe are used for clearing impurities in the tank body, the system is simple in structure and high in safety and consumes little impurity removal time, the impurity removal process and the production process can be performed simultaneously without affecting each other, and the production efficiency is improved.