After initial treatment, maintenance therapy is now commonly used in mCRC patients, which can help patients live longer, have lower side effects, and higher quality of life. The maintenance treatment may include chemotherapy, targeted therapy, or combined with chemotherapy and targeted therapy. But the evidence of cetuximab maintenance is still scant. Methods: We collected real-world data of wild-type RAS unresectable mCRC patients who were treated with cetuximab-based chemotherapy as the first-line therapy between January 2013 and December 2018 at the Zhejiang Cancer Hospital (Hangzhou, China). Results: A total of 177 patients were ultimately included in the study, and 107 patients had progression information in medical records; all patients had survival data. The median OS was 40.9 ms, ORR was 14.7%, and DCR was 73.5%. The subgroup analysis showed that the mOS was better in maintenance patients than in non-maintenance patients (47.1 vs. 28.6 ms, p = 0.001), patients with primary tumor resection had better mOS than who did not (47.1 vs. 35.4 ms, p = 0.038). In those 107 patients who had progression information, the median PFS was 9 ms, the median OS was 42.6 ms, ORR was 18.7%, and DCR was 84.1%. The subgroup analysis showed that the mPFS and mOS were 11.6 and 47.1 ms, respectively, in the maintenance group, which were significantly better than 6.1 ms and 28.7 ms in the non-maintenance group (p = 0.025 and 0.017, respectively). The mPFS and mOS in patients with efficacy evaluation of CR + PR + SD were 10.3 and 47.1 ms, respectively, which is significantly better than 2.8 and 13.5 ms in the PD patients (p = 0.012 and <0.001, respectively). The mOS was best in only lung metastases patients (60.9 ms), then only liver metastases patients (47.1 ms), and then in both liver and lung metastases (42.6 ms); the mOS in patients with other organs metastases was the worst (22.4 ms), p = 0.022. The mOS in male individuals is better than that in female individuals, 60.99 vs. 29.1 ms, respectively, p = 0.042. The primary tumor site and primary tumor resection also affect the OS, primary tumor resection better than did not (not reach the end vs. 35.7 ms, p = 0.048), left side better than right side (47.1 vs. 16.6 ms, p < 0.001), which is consistent with the literature report. There was no statistical difference in other subgroups. Conclusion: For patients with all RAS wild-type and initially unresectable mCRC who experienced standard first-line cetuximab-based treatment and maintenance treatment that contained cetuximab can significantly improve the mPFS and mOS, and the observed toxicity was mostly mild too. So, we consider that cetuximab can be an effective and safety maintenance drug in mCRC patients.