The invention discloses a detection method used for detecting the variety and the quantity of red tide algae. The detection method comprises steps for bipyridine ruthenium oligonucleotide probe labeling, steps for standard curve construction, and steps for sample detection. Specifically, the detection method comprises the following steps: bipyridine ruthenium labeled probes (Bio-NPA-Ru) conduct hybridization reaction with rRNA (ribosomal ribonucleic acid) in target algae cells; after enzyme cutting is conducted by a nucleic acid S1 enzyme, unmatched or dissociative Bio-NPA-Ru probes are removed; after the residual hybridization complexes are denatured, the Bio-NPA-Ru probes with biotin labels are combined with magnetic beads coated by streptavidin; the magnetic beads are absorbed on the surface of an electrode by a magnetic pole below the working electrode; a buffer solution is added with a tripropyl amine solution after redundant components are removed from the buffer solution; and electrochemiluminescence reaction is started under the circumstance that the voltage at the electrode is enlarged, thereby establishing a quantitative relation for quantitative detection of the target algae. The detection method has the advantages of high sensitivity, high reproducibility, continuous testability and short analysis time, is simple and convenient to operate, and is easy to control.