Objective: To investigate the value of CT spectral imaging in evaluation of Crohn's disease activity. Methods: Fifty four patients with Crohn's disease undergone dual phase spectral CT imaging and confirmed by pathology in our hospital from Aug 2015 to Sep 2016 were enrolled. The normalized iodine concentration and normalized water concentration and the slope of spectral curve of bowel wall of arterial phase and portal venous phase at active stage and remission stage were analyzed by t test. And ROC curves of above mentioned variables with statistical difference were calculated and compared. Results: In CT spectral imaging, the arterial phase and portal venous phase normalized iodine concentration at active stage were higher than those at remission stage [(0.228±0.100) g/L vs. (0.097±0.045) g/L, P<0.05; （0.530±0.097） g/L vs. (0.252±0.063） g/L, P<0.05, respectively]. The portal venous phase normalized water concentration at active stage was higher than that of normal control [0.232±0.068） g/L vs. （0.009±0.013） g/L, P<0.05]. The arterial phase and portal venous phase slope of spectral curve at active stage were higher than those at remission stage [2.749±1.051 vs. 1.069±0.457; 3.638±0.724 vs. 1.653±0.687, respectively]. The AUC of arterial phase and portal venous phase normalized iodine concentration for differentiation of active and remission stages were 0.965 and 0.998, respectively; the AUC of portal venous phase normalized water concentration for differentiation of active and remission stage was 0.746 ; the AUC of arterial phase and portal venous phase slope of spectral curve for differentiation of active and remission stage were 0.964 and 0.972,respectively. Conclusions: CT spectral imaging can quantitatively differentiate active and remissive stage of Crohn's disease, and the arterial phase and portal venous phase normalized iodine concentration and the slope of spectral curve in both phases are valuable parameters for differentiation of active and remission stages.