Abstract: objective: To investigate the relationship between nodules size and blood content in patients with lung tumors by spectral computed tomography and the gemstone spectral imaging(GSI) viewer. Methods: During the period from August 2014 to June 2015, 40 patients with 46 lung nodules were collected in the first hospital of China medical university. The were divided the 46 nodules into three groups based on maximum diameter(small,<2 cm, 16 cases; medium,>2 cm~≤3cm, 15 cases; large,>3 cm,15,cases). All patients received biphasic pulmonary enhanced CT scan with GSI mode on a MDCT(Discovery CT 750 HD, GE healthcare). The region-of-interest was placed on the tumor's maximum section, and the mean CT value, water density and iodine density were measured. The difference between the mean values of variables was assessed with one way ANVOA. Pearson's product-moment correlation coefficient(r) was used to study the relationship between the CT values and the material densities. Results: The mean value of iodine density was significantly lower in larger tumors. The mean iodine density in arterial phase and venous phase in tumors of ≤ 2 cm, 2~3cm, and>3 cm were(17.45 ±4.56),(12.05 ±4.89),(10.31 ±5.76)(100 μg/cm³),(18.32 ±3.59),(14.05 ±4.13),(12.82 ±4.58)(100 μg/cm³), respectively. Significant difference in average iodine density was noted between tumors of from 2~3 cm and ≤ 2cm(P<0.05), and between those of>3 cm and ≤ 2 cm(P<0.05). There were no statistically significant differences in mean CT value and water density among three groups. The average CT value and water density were obviously influenced by air, but the average iodine density was unaffected. The average CT value and water density of the GGO-type tumors and solid-type tumors in arterial phase were(-323.83 ±220.27),(43.63 ±15.02)(HU),(638.47 ±227.07),(1 017.27 ±15.23)(100 μg/cm³)(P<0.05), respectively. The average iodine density of the GGO-type tumors and solid-type tumors were(12.86 ±5.92),(12.70 ±4.28)(100 μg/cm³)(P>0.05), respectively. Conclusion: With the increasing of tumor size, iodine density decreases gradually; The average water density were significantly related with CT value, but the average iodine density and the average CT value were no correlation. So the average iodine density is more accurate to indicate the blood content of tumors than mean CT value.