Electrochemiluminescence (ECL) co-reaction and ECL resonance energy transfer (ECL-RET) are two main methods for enhancing the ECL efficiency. In this work, a novel tris(bipyridine) ruthenium(II) derivative (Ru(bpy)(mcbpy)-PEI-ABEI) with high ECL efficiency due to the binary intramolecular ECL self-catalyzed property including intramolecular co-reaction and intramolecular ECL-RET, was prepared for the construction of immunosensor. Firstly, through intramolecular co-reaction, polyethyleneimine (PEI) with large amount of amine co-reactive groups (primary, secondary and tertiary amine) not only increased the ECL intensity of Ru(bpy)(mcbpy), but also improved the ECL signal of N-(aminobutyl)-N-(ethylisoluminol) (ABEI). Meanwhile, ABEI, as an effective energy transfer donor, could further increase the ECL intensity of Ru(bpy)(mcbpy) (as energy transfer receptor) by intramolecular ECL-RET. It is worth noting that the strategy combined intramolecular co-reaction and intramolecular ECL-RET in the same ECL process was more effective for ECL efficiency enhancement compared with the traditional intermolecular interaction or individual intramolecular interaction, which would improve the sensitivity of immunosensor obviously. Thus, the proposed signal-on ECL immunosensor using convex hexoctahedral Pd@Au core-shell nanocrystals (Pd-Au HCDs) as immobilized platform exhibited a detected range for collagen type IV (Col IV), a typical biomarker of diabetic nephropathy (DN), from 0.5pgmL to 7.2ngmL with an estimated detection limit of 0.17pgmL. The developed strategy combined intramolecular co-reaction with intramolecular ECL-RET offered an effective mean for ECL methodology in ECL efficency enhancement and also provided possible road for early diagnosis and treatment monitoring of DN.