Poly(ADP-ribose) polymerase 1 (PARP1) inhibition, increasing chemosensitization and conferring independent antiproliferation against defective homologous recombination cells, has provided a unique opportunity for anticancer therapeutic intervention. Therefore, PARP1, the best characterized enzyme among PARP family, is presently serving as a well-established target for the treatment of oncology attributed to its intimate role in DNA repair. Nowadays, intensified medicinal chemistry efforts have led to the discovery of 12 PARP1 inhibitors that have been advanced into clinical trial. In this article, we classify these candidates as three categories based on the chemical structure, including lactam type, pseudo ring type and untypical PARP1 inhibitors, for a sequential overview of them. In particular, the development of some candidates will serve the purpose for the future exploration of PARP1 inhibitors.