Pre-bored grouted planted pile is a new type of eco-friendly pile foundation. The combination of the lower section of PHC nodular pile and the pile base expansion greatly improves the vertical bearing capacity of single pile. A lot of application practices have been achieved in Jiangsu, Zhejiang and Shanghai regions, but limited to the current research status, the bearing capacity of enlarged grout base is not clear. Based on the in-situ self-balanced loading test, the ultimate compressive bearing capacity of the enlarged grout base of the pre-bored grouted planted pile is investigated. The research results reveal that the measured ultimate bearing capacity of the enlarged grout base of the pile is 40% higher than that calculated by the specifications. The back analysis of the test results shows that the ultimate end resistance reduction coefficient of Shanghai ⑦ layer of silt is 0.72-0.81, which is significantly higher than the recommended value of 0.50-0.55 in the specifications. The bearing capacity of the enlarged grout base of the pile is mainly controlled by the end bearing capacity, and the required displacement value for its full bearing capacity is about 0.03 times the pile diameters. The enlarged grout base of the pile accounts for 64% to 67% of the bearing capacity of pre-bored grouted planted pile, and the structural integrity of the enlarged grout base plays a key role in the working performance of the pre-bored grouted planted pile.