Abstract： Objective To evaluate the application value of spectral curve in gemstone spectral imaging ( GSI ) in evaluating the differentiation state of gastric cancer.Methods Triple-phase enhanced GSI CT scanning was performed on 65 gastric cancer patients whose differentiation state was later confirmed through gastroscopy.The 101 monochromatic image sets obtained with spectral CT imaging were analyzed with the GSI Viewer software.CT values at 40, 70 and 140 keV images were measured to calculate the slopes for spectral curve in the 40-140, 40-70 and 70-140 keV energy range.They were divided into 3 groups based on the pathological results and the corresponding slope measurements were compared with independent t test.Receiver operating characteristic curves were generated to determine the parameters for optimizing sensitivity and specificity in differentiation state of gastric cancer. Results As verified pathologically, there were 21 well-differentiated, 22 moderately-differentiated and 22 poorly-differentiated adenocarcinoma cases.The slope for spectral curve was larger at the foci of gastric cancer than that in normal gastric wall:the lower differentiation state, the larger the slope.During the arterial phase, the slope of the normal gastric wall , well-differentiated adenocarcinoma , moderately-differentiated adenocarcinoma and poorly-differentiated adenocarcinoma in the 40-70 keV energy range was 1.78 ±0.12,1.86 ±0.30,1.87 ± 0.28,2.59 ±0.31,the slopes of well and moderately-differentiated adenocarcinoma and normal gastric wall were significantly different from poorly-differentiated adenocarcinoma in the 40-70 keV energy range ( P< <br> 0.05), but were not different in the other 2 energy ranges (P>0.05); during the portal vein phase, the slope of the normal gastric wall, well-differentiated adenocarcinoma, moderately-differentiated adenocarcinoma and poorly-differentiated adenocarcinoma in the 40-70 keV energy range was 3.30 ±1.13, 3.96 ±0.29,4.10 ±1.28,4.98 ±2.15,the slopes in all 3 energy ranges were significantly different in each group (P<0.05).Using the slopes in the 40-70 keV energy range, the sensitivities and specificities for determining the differentiation states were >81%and >86%respectively during the arterial phase and >72%and >72% during the portal venous phase.Conclusion The spectral curve at the foci of gastric cancer was correlated with the histological differentiation state.And the slope of spectral curve of GSI may offer a new index for evaluating the differentiation state of gastric cancer before operation.