To clarify the time-dependent evolution of pile-soil interaction and the variation law of negative skin friction for pile foundations in high loess fill sites, and to elucidate the influence of internal force variation on the long-term service performance of pile foundations, considering the creep deformation of backfilled loess, the finite difference software FLAC3D was employed with the Burgers model to simulate the creep characteristics of backfilled loess. The time-dependent evolution of internal forces, displacement, and the neutral point of rock-socketed pile foundations was analyzed under varying pile diameters. Based on the effective stress method, a correction was made to the formula for negative skin resistance of pile foundations after creep stabilization in high fill sites, which is lacking in current codes. The results indicate that pile shaft displacement lags behind the settlement of the surrounding backfilled soil, and changes in pile diameter induce significant increments in settlement and internal forces of the pile foundation. The axial force in the pile after creep stabilization differs substantially from that without creep consideration. The negative skin friction coefficient for pile foundations in high fill sites after creep stabilization is approximately 0.30 to 0.61 times the pile diameter, leading to a more pronounced reduction in pile bearing capacity and, in severe cases, endangering the long-term safety performance of pile foundations in high backfill sites.