The invention discloses a conduction filtering diagnosis device which is formed by combining one or more sub-modules. Each sub-module comprises two device jacks, a cascade jack, a cascade plug, a fixed mortise and a fixed tenon; the sub-modules can be cascaded to form a cascade path according to the filtering grade requirement so as to provide multilevel filtering; according to the number of wiresof a wire harness to be filtered, the cascade paths can be connected in parallel to form a parallel path, and multi-path filtering is carried out; the combined conduction filtering diagnosis device is connected to the wire harness to be filtered, and required filtering devices are inserted between different device jacks, thereby on-line rapid conduction filtering diagnosis in multiple combinationforms is provided.