The utility model relates to a single mechanical sealing device. The single mechanical sealing device comprises a sealing face formed by a movable ring arranged on a shaft and a static ring arranged in a static-ring base, wherein the movable ring is fixed to the shaft through a movable ring fixing component, and an auxiliary movable ring sealing ring is arranged between the movable ring and the shaft to form a static sealing point; the static ring is connected with a spring component through a static ring fixing component, and an auxiliary static ring sealing ring is arranged between the static ring and the inner wall of the static ring base to form a static sealing point; the spring component is arranged between the static ring fixing component and a spring base, and the static ring and the movable ring are closely bonded to form a movable sealing point through the spring force action of the spring component. According to the single mechanical sealing device, when equipment runs, the spring component is not in contact with materials, influences brought by the contact between springs and the materials are effectively avoided, and the single mechanical sealing device is good in using stability and strong in reliability in the material occasion where crystallization is easy to achieve.