Large diameter and super-long pile has found abroad application in high buildings, super high buildings, large bridges and port engineering, and its ultimate bearing capacity is increasingly demanding. Its ultimate bearing capacity is affected by many kinds of uncertainty factors, which is a complex grey analysis program. The influencing factors are analyzed by grey system theory such as pile diameter, pile length, socket length, the length to diameter ratio, the socket length to diameter ratio, rock strength and rock coefficient of weathering. The grey correlation analysis is combined with the tested statistical data of 19 large diameter and super-long piles in Zhejiang province based on the grey correlation model. With the objective to overcome the lack of objectivity in calculating correlation degree of the grey correlation analysis, this paper has improved the calculated formula of the correlation degree based on the distance analysis method. The paper has get and compared the corresponding result of the correlation degree and its rank of various influence factors with the improved calculated formula and the original formula respectively. The influence advantage factors found by grey correlation analysis, and the results can provide important reference for the future theoretical research and design application of large diameter and super-long pile, and show that the grey correlation method is effective and reliable.