To ensure better horizontal deformation resistance, the pile foundation of integral abutment jointless bridges (IAJBs) should be designed as flexible pile. However, the calculation algorithm of flexible pile in relevant codes in China is mainly applied to the laterally loaded pile, and whether it can be used to identify the flexible pile for IAJBs remains a tricky issue to be studied. Therefore, in order to study the aseismic performance and interaction mechanism of the single pile–soil system, three concrete model piles with different lengths were tested under horizontal low-cycle reciprocating displacement based on a specially designed pile deformation measurement method. The result shows that the earliest cracking position of concrete pile is between 3–6 times of pile diameter. The deeper the pile is buried, the better the effect of pile–soil interaction with a deeper location of the deformation characteristic point. Meanwhile, stiffness of pile–soil system, horizontal ultimate bearing capacity and aseismic performance is improved with burial depth increased. The result also indicates that, when the pile–soil system reach the elastoplastic stage, the flexible performance of the pile will gradually degenerate from the elastic pile to the rigid pile. Furthermore, the provisions in relevant codes in China are not safe enough when evaluating the flexural performance of the pile foundation of integral abutment jointless bridges. Hence, it is recommended to use the Broms method for the benchmarking calculation in practical engineering.