Background: Although the preexisting diabetes mellitus (DM) is known to have a high risk for death in many cancers, its impact on the mortality for the colorectal cancer (CRC) patients is still uncertain. In this study, we conducted a meta-analysis to explore an association of DM with the survival for the CRC patients. Materials and Methods: We made a relative data search from the public available databases including Medline and Embase with a cutoff date to Jan 31, 2017. Pooled hazard ratios (HRs) were calculated using either a fixed or random effect model. Trim and fill analysis was conducted to test and adjust for publication bias. Subgroup analyses were also performed for overall survival and all-cause mortality when stratified by tumor stage, geographical region, duration of follow-up, gender and subsite of cancer. Results: Twenty-one eligible cohorts including 1,025,034 patients were identified and included in this meta-analysis review. The sample size for each analysis was ranged from 207 to 771,297 patients. It is revealed that with the preexisting DM, the CRC patients had a significantly increased all-cause mortality (pooled adjusted HR: 1.23; 95% CI: 1.11, 1.37) and decreased overall survival (pooled adjusted HR: 1.25, 95% CI: 1.19-1.31). But no difference was found for adjusted cancer-specific survival for the CRC patients with the preexisting DM compared with subjects without DM. These associations almost remained consistent after trim and fill adjustment and across those outcomes when stratified by site of cancer, tumor stage, population geography, study design, duration of follow-up, data resource or gender. Conclusions: This meta-analysis review indicates that preexisting diabetes mellitus in CRC patients is severely associated with the worse overall survival but not with cancer-specific survival.