The invention discloses a ruthenium complex for inhibiting DNA topoisomerase, which has a molecular formula of [RuL2(PZPP)]Cl2, wherein L is 2,2-bipyridine or 1,10-o-phenanthroline, and PZPP is 3-(2-pyrazinyl)-1,2,4-triazolo[4,5-e]pyrene. The invention also provides the preparation method of the ruthenium complex. The invention further provides a compound 3-(2-pyrazinyl)-1,2,4-triazolo[4,5-e]pyrene obtained in the preparation process of the ruthenium complex. The invention also discloses the application of the ruthenium complex for inhibiting DNA topoisomerase in the preparation of anticancer drugs. The ruthenium complex for inhibiting DNA topoisomerase has good water solubility and has double effects on inhibiting type-I DNA topoisomerase and type-II DNA topoisomerase, and both of the IC50 values are less than 1 muM. The ruthenium complex has wide application prospect.