The preparation process of Ru(II)-polypyridine complex includes the following steps: preparing 1,10-phenanthroline-5,6-diquinone, pyridine [3, 2-a:2', 3'-c] phenazine as ligand I, and 7,8-dimethyl pyridine [3, 2-a: 2', 3'-c] phenazine as ligand II, Ru(bipy)2Cl2.2H2O (bipy=2, 2'-dipyridyl) as precursor I and Ru(phen)2Cl2.2H2O as precursor II; adding certain amount of Ru(bipy)2Cl2.2H2O/Ru(phen)2Cl2.2H2O, ligand I/ligand II, and mixture liquid of methanol and water, heating reflux for certain time, heating to concentrate, adding water and boiling, freezing, adding sodium tetrafluoborate, filtering and separating out precipitate, re-crystallization in alcohol, and stoving under infrared lamp to obtain the Ru(II)-polypyridine complex. The Ru(II)-polypyridine complex is used as nucleic acid recognizing probe for the analysis and detection of nucleic acid, and has high stability, high sensitivity, high selectivity and other advantages.