Pile–anchor structures are widely used in foundation excavation and slope reinforcement due to their safety and reliability. However, the pile–anchor structures have the common problem of the prestress loss of anchor cables, which may reduce the stability of the structures. To accurately predict the prestress loss of anchor cables, a new prestress loss calculation model was established, and the availability of the prestress loss calculation model was verified through engineering cases. Meanwhile, aiming at the long-term prestress loss of anchor cables, the coupled creep behavior of anchor cable–rock and soil was studied and an anchor cable–rock and soil coupled creep model suitable for pile–anchor structures is proposed. The model test confirms that the coupled creep model could accurately describe the coupled creep behavior of the anchor cable and the rock and soil mass. The models provide a theoretical basis for the study of the prestress of anchor cables in pile–anchor structures, and have a guiding significance for the design and construction in foundation excavation and slope engineering.