Abstract: In order to evaluate the value of 18FDG-PET in the diagnosis and staging of colorectal carcinoma, 24 patients with potentially colorectal carcinoma are made 18FDG-PET examination. The results shows that The primary tumour is visualized in 95% with PET（SUVmax＝7.09±3.26，2.98~12.2）. Distant metastases are found in eight patients entirely. For local-regional lymph nodes the sensitivity is 50%, the specificity is 100%. 33% of patients are facilitated in the treatment planning. 18FDG-PET can detect primary colorectal carcinomar and metastasis of lymph node, liver, bone sensitively. 18FDG-PET is of little use for determinant of T stage. 18FDG-PET is useful in the staging and treatment of colorectal of carcinoma.