The invention discloses a grain drying and dehumidifying heat pump unit and a grain drying circulation heat pump system. According to the technical scheme, the grain drying and dehumidifying heat pump unit and the grain drying circulation heat pump system comprise a drying chamber, a drying cavity is formed in the interior of the drying chamber, a drying and dehumidifying mechanism is arranged in the interior of the drying cavity, a circulation preheating mechanism is arranged on one side of the drying chamber, the drying and dehumidifying mechanism comprises an exhaust pipe, the exhaust pipe is arranged in the interior of the drying cavity, the two ends of the exhaust pipe both penetrate through the drying chamber, the exterior of the exhaust pipe is provided with a material blocking cover plate in a sleeved mode, the two ends of the material blocking cover plate are fixedly connected with the side wall of the drying cavity, the exterior of the material blocking cover plate is provided with a disc in a sleeved mode, and one side of the disc is fixedly connected with an annular inner gear. The grain drying and dehumidifying heat pump unit and the grain drying circulation heat pump system have the beneficial effects that the influence and pollution to the environment during grain drying are reduced, the labor intensity during grain drying is reduced, the automation degree of the drying process is improved, meanwhile, the hot air pushing efficiency is high, the drying efficiency is high, hot air circulation conveying is achieved, the hot air utilization rate is improved, and energy conservation and environment protection are achieved.