The disclosure provides a method for evaluating whether an individual with cancer is suitable for being administered with anti-cancer drugs. Wherein the anti-cancer drug is a CDK inhibitor. The method includes the following steps: (1) detecting a copy number of a first gene and a copy number of a second gene from an in vitro sample of the individual with the cancer to obtain a copy number variation (CNV) of the first gene and a copy number variation (CNV) of the second gene; (2) calculating a copy number variation ratio (CNV ratio) between the copy number variation (CNV) of the first gene and the copy number variation (CNV) of the second gene, wherein the first gene encodes a cyclin and the second gene encodes a cyclin dependent kinase inhibitor (CDKN); and (3) determining whether the individual with the cancer is suitable for being administered with the CDK inhibitor according to the CNV ratio.