The invention discloses an automatic guardrail cleaning device which comprises a group of water injection system and two groups of chain-type washing brush devices. A water pump is arranged above a water tank; a DC (direct current) motor is fixedly arranged at one side of the water tank; the DC motor is connected with V-belt transmission mechanisms through couplings; the V-belt transmission mechanisms are connected with chain transmission mechanisms; washing brushes are arranged on the chain transmission mechanisms; spray nozzles are arranged at one sides of the chain transmission mechanisms by the water tank through pipelines; electromagnetic clutches are arranged between the V-belt transmission mechanisms and the chain transmission mechanisms; and the washing brushes are fixedly arranged on outer chain plates on the chain transmission mechanisms and are connected with nuts through screws. By cooperative using of the water injection system and the chain-type washing brush devices, the automatic guardrail cleaning device not only can be used for cleaning guardrails on the street, but also can be used for cleaning guardrails in narrow places, is driven by adopting electric energy and is more environmental-friendly.