The bearing capacity of a pile foundation in Zhanjiang group structural clay under vertical loads was studied based on in situ model tests. In single pile in situ model tests, six groups of pile models with the same material and diameter but different depths in soil were selected, and the slow maintained load method was used. The load-settlement curve, axial force distribution along the pile shaft, and side friction varying with the depth in soil of single piles were obtained. Under vertical loads, the load-settlement curves of all six groups of single pile models in the Zhanjiang group structural clay show sharply declining trends, with yielding points occurring at the ultimate limit state, and the vertical ultimate bearing capacity increases with the length-diameter ratio of the single piles; under constant loads, with the increase of the length-diameter ratio, the settlement at the pile top gradually decreases at a slowly decreasing rate; under large loads, the decreasing rate of resettlement at the top of super-long piles, according to the load-settlement curve, is almost zero, and there exists an effective pile length; and under a constant level of loads at the pile top, the proportion of the pile end resistance to the total load at the pile top gradually decreases with the increase of the length-to-diameter ratio, with the maximum value decreasing from 29.8% to 0.8%, while the side frictions of single piles with different depths in soil under ultimate loads change little, with a stable value of about 40kPa.