Objective To explore the relationship between circulating tumor DNA（ctDNA） state

mutation gene and prognosis in patients with advanced colorectal cancer after failure of chemotherapy. Methods Collect 10 ml of peripheral blood of 83 patients with advanced colorectal cancer who failed to receive chemotherapy

and customized Geneseq one NGS panel covering 416 tumor related gene probes were used to hybridize and enrich. After highly efficient capture

polymerase chain reaction（PCR） amplification was carried out

and the target enriched library was sequenced on the hillseq ngs platform（Illumina）. Results Among 83 patients with advanced colorectal cancer after chemotherapy failure

tumor related mutations were found in 54（65.06%） patients

involving a total of 152 genes. The top 20 genes including APC

TP53

KRAS

PIK3 CA

etc. were screened according to the mutation frequency

ctDNA mutation frequency

tumor mutation burden（TMB）

KRAS and PIK3 CA were significantly correlated with prognosis（P<0.05）. Clinical correlation analysis showed that liver metastasis was strongly correlated with multiple undesirable mutations in tumor genes（P<0.05 or P<0.01）. There was a significant correlation between spleen kidney deficiency syndrome and ctDNA mutation frequency

TMB

TP53（P<0.05）

and there was a significant correlation between yin syndrome

yang syndrome in eight syndrome differentiation and TMB（P<0.05）. Conclusion Peripheral blood ctDNA can well reflect the molecular biological status of patients with advanced colorectal cancer after chemotherapy failure by TCM syndrome differentiation treatment. Spleen-kidney deficiency syndrome is related to lower ctDNA mutation frequency and lower tumor suppressor gene mutation. Patients with yin syndrome have lower TMB and patients with yang syndrome have higher TMB.