The invention relates to the field of genetic engineering and biotechnologic detection, and concretely relates to a gene group and a kit for diagnosing lung cancer, and a diagnosis method thereof. The gene group for diagnosing the lung cancer includes ABCB1, AKT1, ALK, APC, ATIC and other 63 genes. The method using the gene group to diagnose the lung cancer comprises the following steps: (1) extracting free DNA and genome DNA from the plasma of a sample to be detected; and (2) breaking the genome DNA into fragments with the length of 150-250 bp, carrying out hybrid capture on the broken genome DNA and the free DNA to construct a DNA library, carrying out online sequencing, and analyzing the obtained sequencing result. Exon and partial intron regions of the 68 genes of the free DNA are enriched at one time by a probe capture technology to realize multi-gene and multi-target parallel deep high-throughput sequencing with high accuracy, optimize the detection flow and improve the detection precision, so liquid biopsy, low-frequency detection and tumor diagnosis become possible.