Drug resistance is a major problem faced by tumor cell-targeted drugs. Currently, functional gene screening is the most common strategy for screening drug resistance genes. In recent years, Crispr-cas9 gene editing technology has been widely used in the functional studies of tumor-related genes due to their characteristics of accuracy, simplicity and efficiency. The principle of CRISPR-Cas9 Library Screening Technology and its application in functional Gene Screening are reviewed. At the same time, the application prospect of the Crispr-Cas9 technology is forecasted.