Objective To evaluate the diagnostic value of 18F-FDG PET/CT and tumor markers (CEA,CA19-9,CA24-2) in detection for recurrence and metastasis of postoperative colorectal moderately differentiated adenocarcinoma. Methods Fifty-five patients were enrolled in this study. All of the patients were tested with serum CEA within 2 weeks when they underwent 18F-FDG PET/CT scan, and some patients were tested with serum CA19-9 and CA24-2 simultaneously. According to the pathology and clinical results of their follow-up, the sensitivity, specificity, positive predictive value, negative predictive value and accuracy of 18F-FDG PET/CT and tumor markers were calculated based on different divided groups, respectively. Results According to the pathology and the results of their clinical follow-up, the sensitivity of 18F-FDG PET/CT, CEA, CA19-9, CA24-2 and the combination of those three tumor markers were 95.74%, 68.09%, 28.57%, 40.00% and 74.47%, respectively. The specificity of 18F-FDG PET/CT, CEA, CA19-9, CA24-2 and the combination of those three tumor markers were 75.00%, 50.00%, 66.67%, 71.43% and 50.00%, respectively. The positive predictive valueof 18F-FDG PET/CT, CEA, CA19-9, CA24-2 and the combination of those three tumor markers were 95.74%, 88.89%, 85.71%, 88.89% and 89.74%, respectively. The negative predictive value of 18F-FDG PET/CT, CEA, CA19-9, CA24-2 and the combination of those three tumor markers were 75.00%, 26.67%, 11.42%, 17.24%, 25.00%, respectively. The accuracy of 18F-FDG PET/CT, CEA, CA19-9, CA24-2 and the combination of those three tumor markers were 92.73%, 65.47%, 32.65%, 44.68% and 70.91%, respectively. There were 2 cases of false positive and 2 cases of false negative in 18F-FDG PET/CT. Conclusion 18F-FDG PET/CT has high value in detecting recurrence and metastasis of postoperative colorectal carcinoma. Tumor markers have the positive value to imply the recurrence and metastasis of postoperative colorectal carcinoma and are useful to indicate when to perform the 18F-FDG PET/CT. The combination of tumor markers could improve the diagnostic efficiency to some extent.