The invention belongs to the field of pharmacy and relates to application of 3,5-dimethylpsoralen in preparing antitumor medicaments. The molecular formula of the 3,5-dimethylpsoralen is C13H10O3, and the molecular weight is 214.22. The 3,5-dimethylpsoralen has broad-spectrum antitumor activity and strong suppression effect on various human tumor cells in vitro. The mechanism of suppressing the proliferation of hepatocarcinoma HepG2 is cancer cell apoptosis induction, thus the 3,5-dimethylpsoralen can be combined with medicinal dressings and applied to preparing medicaments for resisting tumor activities, particularly to preparing the medicaments for resisting the liver cancer, the breast cancer, the cervical cancer, the skin cancer, the nasopharyngeal carcinoma and the colon cancer. The invention provides more choices for treating the cancers, and the 3,5-dimethylpsoralen has small toxicity to normal cells and is beneficial to clinical application.