CRISPR-Cas9, which is characterized by simplicity, effectiveness and direct targeting, can be used to treat some incurable genetic diseases by editing DNA sequence. In recent years, Crispr-Cas9 has entered cancer clinical trials and has been used to generate genetically modified animal models and develop drugs, which is of great clinical value. This paper reviews the CRISPR-Cas9 system and its application progress in tumor research, including CRISPR screens in the identification of personalized drug targets, delivery systems and adoptive cell therapy. The limitations and prospects of CRISPR-Cas9 in clinical therapy were also discussed, aiming to provide a reference for the future application of this technology for precise cancer therapy.