An ash-collecting and exhaust device for a grain dryer has a body, a fan unit, and a driving unit. The body is a hollow barrel, and has an air inlet, an air outlet, and an internal surface being divergent adjacent to the air inlet. The fan unit is rotatably mounted in the body to enable external air to flow into the body via the air inlet and flow out of the body via the air outlet, and has an external surface being obliquely divergent to form an oblique passage between the body and the fan unit. The driving unit is securely mounted on the body, is connected to the fan unit to enable the fan unit to rotate relative to the body to guide the external air flowing into the body.