A method and a kit for determining genome instability based on next generation sequencing (NGS) are disclosed. The new method is used to determine whether there is homologous recombination defect by calculating a comprehensive value of one or more of pathogenic germline and somatic mutations, such as SNV, indels, and CNVs, and Biallelic germline and somatic mutations, pathogenic mutational signature, copy number variation (CNV) in homologous recombination repair (HRR) gene, genomic structural variation and genome instability. The genomics DNA is interrupted and added with an A adapter; then corresponding polymerase chain reaction (PCR) is conducted, and Whole genome sequencing is performed; the hybrid capture is conducted with designed probes of HRR genes and SNPs, and a captured DNA library is subjected to amplification and library sequencing; and then professional bioinformatics software is used for evaluation to determine the homologous recombination deficiency (HRD) status.