In this work, we designed an ECL ratiometric biosensor with a three-stranded Y-type DNA (Y-DNA) probe and induced a hybridization chain reaction (HCR) for the highly sensitive detection of SARS-CoV-2 nucleic acid. The important component of this system is the self-assembled Y-Shaped probe based on three nucleic acids. Y1, Y2, and Y3 can be linked by complementary base pairing to Hairpin1 (H1), Hairpin2 (H2), and Ru modified DNA (Ru1), respectively. H1 and H2 can trigger the HCR reaction when activated by the SARS-CoV-2 RdRp gene and the 5' end of Ru1. The 5' end of Ru1 is modified with the Ru complex, which can produce a strong electrochemiluminescence luminescence signal at 620?nm under an applied voltage. Through the amplification of Y-DNA-induced HCR reaction, Ru1 on the electrode surface gradually increased, the ECL signal at 460?nm was gradually quenched, and the signal at 620?nm was steadily generated. The SARS-CoV-2 RdRp gene can be quantified according to the degree of decrease of ECL signal at 460?nm and the increase of ECL signal at 620?nm. Combining the two signal amplification strategies, this ratiometric ECL biosensor can accurately and efficiently detect the target gene with a detection limit of 59 aM.