The diagnosis and treatment of tumors have beena hot medical research area for a long time. Terahertz technology has great potential for application in the biomedical field due to its low photon energy, label-free, and high temporal resolution. This paper introduces the application of terahertz technology in tumor diagnosis and treatment. Terahertz tumor diagnosis is mainly based on terahertz spectroscopy and imaging technology. By using terahertz spectroscopy to obtain spectral feature information, with the combination of advanced pattern recognition and machine learning algorithms to extract high-dimensional features, tumors can be detected and diagnosed. The imaging technique mostly utilizes the differences in components between tumor cells and tissues to distinguish and identify tumors. The research on terahertz technology in tumor diagnosis is first introduced in three dimensions: biomolecules, cells, and tissues. The research on biomolecules focuses on tumor markers such as proteins, nucleic acids, amino acids, and glycans. Advanced research in cellular detection focuses on identifying tumor cells and detecting blood cells. Regarding tissue, the detection and diagnosis of cancer tissues with different types is presented in two main dimensions: imaging and terahertz time-domain spectroscopy. The research on tumor therapy based on terahertz technology emphasizes the positive effects, including biological effects on ablation of tumor cells and modulation of gene expression to improve body functions. Finally, the current limitations and prospects of terahertz technology in biomedical applications are discussed to provide insights for future research on terahertz in related fields.