Objective: To study the influence of contrast agent on CT value of tissue around syringe with different concentrations of contrast agent in the paraffin mold. Methods: Paraffin phantom of syringe with 11 different concentrations of contrast agent and saline as control was scanned with the same condition, and the CT value of the study area was measured in pixels and analyzed. Results: Contrast concentration had impact on CT value of different areas. CT beam hardening effect decreased the CT value of the small area around blood vessels with the increase of contrast agent concentration. Volume effect increased the CT value of area outside the beam hardening effect around blood vessels with the increase of contrast agent concentration. Conclusion:　CT values of surrounding tissue increase because of volume effect. There is significant difference between each experimental group and control group(P<0.004). Decreases of CT value of peripheral tissue due to pixel tube beam hardening effect is not significant between each experimental group and control group(P>0.004).