Inclusion Criteria:  Age ≥ 18 and ≤80 years old, regardless of gender; Personal status (PS) score as over 80 or Eastern Cooperative Oncology Group (ECOG) score as 0 ~ 2; Pathologically confirmed as stage III colorectal cancer; Radical operation performed ; With expected survival of more than 12 months; The subjects (or their legal representative / Guardian) must sign the informed consent form, indicating that they understand the purpose of the study, understand the necessary procedures of the study, and are willing to participate in the study.  Exclusion Criteria:  Neoadjuvant therapy performed before operation; Blood transfusion performed during operation or within 2 weeks before operation; Incomplete baseline samples, including preoperative plasma samples, surgical tumor tissue samples and plasma samples 3-7 days after operation; Two consecutive test points missing or three plasma samples missing in total before a positive ctDNA time point Pregnant or lactating women who have fertility and do not take adequate contraceptive measures; Have a history of other malignant tumors within 5 years, except cured cervical carcinoma in situ or non melanoma skin cancer; Primary brain tumor or central nerve metastasis is not under control, with obvious intracranial hypertension or neuropsychiatric symptoms; Patients with the following serious or uncontrollable diseases: severe heart disease, the condition is still unstable after treatment, including myocardial infarction, congestive heart failure, unstable angina pectoris, pericardial effusion with obvious symptoms or unstable arrhythmia within 6 months before enrollment; definite neuropathy or psychosis, including dementia or seizures; severe or uncontrolled infection; active disseminated intravascular coagulation and obvious bleeding tendency; Significant impairment of important organ function; Other conditions in which the investigator believes that the patient should not participate in this trial.