Grey correlation degree calculation model which reflects the positive and negative relation of sequences is applied to calculate the relevant influence factors on the natural circulation and heat transfer of LBE(Lead Bismuth Eutectic). Results show that in the range of selected parameters: temperature difference, height difference and tube diameter show positive correlation with the velocity and heat transfer of LBE. And within a certain range, the influence of temperature difference is larger than the influence of height difference, and the influence of height difference is larger than the influence of tube diameter, but there is little difference about the numerical of grey correlation degree, it means that the impact almost equal.