Abstract: The base post-grouting is used to improve the base resistance of piles, and the mechanism of base post-grouting in super-long piles needs to be a deep studied. In order to study the bearing capacity, static load tests are carried out on super-long bored piles employed in great bridges. The differences of the bearing capacity of super-long piled before and after base grouting are analyzed. Based on the test results, it is found that the bearing capacity of piles is increased by over 10 percent after base grouting. The frictional resistance at the lower part of piles increases significantly. As the load increases, the role of base grouting is more obvious. A comparative study between the field measured and calculated increments of the bearing capacity is made. The results indicate that the calculated increments of domestic standards are smaller than the field measured increments, and some calculated increments are over-conservative.