The invention relates to a CRISPR/Cas9 enrichment sequencing method applied in large-scale screening of cancer genes. Firstly, an sgRNA library is established; then the sgRNA library is packaged by lentiviruses, and viruses are collected; the sgRNA library is screened in a cancer cell line, the obtained cells are extracted and screened, and genome DNAs of precancerous cells are screened; finally, enrichment of sgRNAs in the genome DNAs is carried out. When the provided method is compared with the prior art, the screening process of CRISPR/Cas9 cells is improved, the virus infection efficiency is determined and the virus MOI value is determined through a simple method and by utilization of puromycin resistance of infected cells, importantly, the restriction enzyme cutting method and a high flux method are combined, correct chromatin fragments can be obtained effectively, false positive caused by non-specific PCR amplification can be lowered, a DNA template of sgRNAs can be amplified efficiently, and a library establishment efficiency is raised.