This study explored the value of the detection of serum methylated septin 9 (mSEPT9) and carcinoembryonic antigen (CEA) in the auxiliary diagnosis, curative effect evaluation, and follow-up monitoring of colorectal cancer (CRC). The diagnosis and treatment data of 208 CRC patients in the First Affiliated Hospital of Xinjiang Medical University (China) were collected from March 2019 to December 2019, and these patients were followed up. The correlation between serum CEA, mSEPT9 levels, and tumor location and size were analyzed. Serum mSEPT9 and CEA were detected before and after surgery and during follow-up after treatment to analyze the value of mSEPT9 in efficacy evaluation and follow-up monitoring. In 87 patients with CRC patients who underwent surgery, the average size of poorly differentiated tumors was the largest (25.01±14.08 cm2), which was significantly different from that of moderately differentiated tumors (P =0.039). There was a statistically significant difference in serum CEA level among different degrees of differentiation (P=0.018). The level of CEA was relatively low when tumors occurred in the transverse and ascending colon. When the level of CEA was high, negative mSEPT9 suggested that the probability of a tumor occurring in the cecum was high; positive mSEPT9 indicated that the tumor was highly likely to occur in the descending or sigmoid colon. Detection before and after surgery revealed that the level of mSEPT9 may be related to the tumor-bearing state of patients. A Follow-up study also showed that the sensitivity and specificity of mSEPT9 for recurrence and metastasis were 83.3% and 97.7%, respectively, and the sensitivity and specificity of CEA were 61.1% and 89.5%, respectively. The combined detection of mSEPT9 and CEA can indicate the location and size of colorectal cancer, while the detection of serum mSEPT9 may have clinical significance in the efficacy evaluation and follow-up monitoring of colorectal cancer.