Disclosed are an azaphenalene-3-one derivative, its preparation method and its application, in the field of pharmaceutical synthesis. The derivative has the following Formula (I), wherein R is H, 2-fluoroethylamino, 2,2,2-trifluoroethylamino, diethylamino, pyrrolidinyl, imidazolyl, piperidinyl, morphinolinyl, 4-methylaminopiperidinyl, 4-dimethylaminopiperidinyl, (1-methylpiperidin-4-yl)methylamino, (1-phenylpiperidin-4-yl)methylamino, (1-benzylpiperidin-4-yl)methylamino, or 7-fluoro-3,4-dihydroisoquinoline-2(1H)-yl. The preparation method of the azaphenalene-3-one derivative is simple, the yield is high, post-treatment is easy, and purity is high. The derivative has high inhibitory activity against PARP enzyme. It establishes a foundation for researching better anti-tumor drugs using PARP inhibitors.