Background: Tumor mutation burden (TMB) is new clinical marker that predicts responses to immunotherapy, but the molecular basis of TMB is unknown. Understand the association between genomic landscape and TMB may help to a better guidance of immunotherapy. Methods: We performed a retrospective review of 513 non–small-cell lung cancers (NSCLC) patients. Tumor tissues were acquired from initial diagnosis before any drug treatment and sequenced by Next Generation Sequencing (NGS) of 1021 genes. TMB (mutations/Mb) was analyzed as the number of somatic non-synonymous base substitution and indel per Mb in coding region. The top quartile was classified as TMB high. Results: A total of 513 patients had an average TMB of 7.5 mut/Mb. The median TMB was 5.8 mut/Mb (range, 1 to 67.68 mut/Mb). 128 patients were assessed as TMB high (TMB-H) and 385 patients were TMB low (TMB-L). The median TMB was 14 and 4.32 mut/Mb for patients with TMB-H and TMB-L respectively. EGFR mutations were detected in 28 patients with TMB-H (21.9%) compared with 228 with TMB-L (59.2%; P< 0.01). And other known drivers were significantly more common in patients with TMB-L than with TMB-H, which included ALK fusion, ROS1 fusion, MET splice and BRAF V600E (P< 0.01). KRAS and TP53 mutations were more common in patients with TMB-H than with TMB-L, but no significant difference of KRAS mutations were found between TMB-H and TMB-L (12.5% vs 7.8%; P = 0.15). Significant differences of TP53 mutations were found between TMB-H and TMB-L (81.3% vs 54.8%; P < 0.01). In addition, alterations of homologous recombination repair and mismatch repair gene were more likely to be the high TMB, e.g. alterations in BRCA1, BRCA2, ATM, ATR, PMS2 and MSH2 were significantly enriched in patients with TMB-H. Conclusions: TMB-H is associated with lack of current druggable oncogenic drivers, such as EGFR mutations/ ALK or ROS1 fusion. TMB detection provides a clinically useful predictor of response to immunotherapy. TP53 and KRAS mutations specifically enriched in patients with TMB-H, may be served as potential predictive factors in guiding immunotherapy. Lastly, DNA damage repair mutations strongly correlated with high TMB, and may be a primary molecular mechanism for TMB.