Colorectal cancer (CRC) is a common cancer that threatens human health, with the incidence ranking the third in the world. 70% of patients are in the middle and late stages whendiagnosed, and even after radical surgery, 30% - 50% of patients with CRC have recurrence or metastasis after radical surgery. Therefore, after radical surgery and adjuvant chemotherapy, regular monitoring of CRC patients should be paid attention to in order to detect the recurrence and metastasis lesions that can be resected and the early non-invasive metachronous multiple primary tumors. The sensitivity of FIT-DNA to CRC was 95.5%, the sensitivity to advanced adenoma (AA) was 63.5%, and the specificity was 87.5%, showing a good ability to screen colorectal cancer and precancerous lesions. At present, there is no report on the application of FIT-DNA combined detection technology in the high-risk recurrence period and mid - and long-term monitoring after CRC surgery in China. In this study, Fit-DNA combined detection technology was applied to the follow-up monitoring of patients after CRC surgery, so as to optimize the current typical postoperative follow-up strategy, find early recurrence and multiple primary colorectal tumors after CRC surgery, seek the best postoperative follow-up model, improve the compliance of patients to follow-up, and ultimately benefit survival. Detailed Description:Outline:This study was a single-center, observational study. Fit-DNA detection technology was used as a target method, and colonoscopy was used as the gold standard control to follow up and monitor patients with colorectal tumors after surgery, and to explore whether it is an effective non-invasive auxiliary method for monitoring CRC recurrence and metastasis and multiple primary colorectal tumors.