The invention relates to an in-situ online anticorrosion method and device for a petroleum hydrocarbon device and a pipeline. The in-situ online anticorrosion method comprises the following steps of: heating the petroleum hydrocarbon device or pipeline in contact with hydrocarbon substances to 200-800 DEG C, and holding for 1-240h to ensure that a coke film is formed on the inner surface of the petroleum hydrocarbon device or pipeline. The in-situ online anticorrosion device provided by the invention comprises a heating sleeve and heating equipment; the heating sleeve is provided with a heating medium inlet and a heating medium outlet and can be spirally wound on the outer surface of the petroleum hydrocarbon device or pipeline; and the heating equipment is used for heating the heating medium. The coke film generated by using the in-situ online anticorrosion method provided by the invention is smooth and compact, stable in chemical property and capable of isolating corrosive substances in petroleum hydrocarbon from being in contact with the inner surface of the petroleum hydrocarbon device or pipeline, playing an anticorrosion role and ensuring long-period safe operation in a flow boundary layer of the inner surface of the petroleum hydrocarbon device or pipeline.