In order to study the influence of different materials on the prestress loss law of anchor cable, based on the deep foundation pit project of Pile-anchor support in Qingdao Haitian Center, combined with the field measurement and ABAQUS finite element numerical simulation, the variation law of anchor cable prestress under the action of three different materials of waist beam was explained, and the simulation results were compared with the measured results. The results show that the simulated results are basically consistent with the measured ones. The prestress of anchor cable changes gently with time, which can be divided into three stages: rapid decline, stable change and basic stability. During the loading process, the anchor cable stress is transferred from the free section to the anchorage section, and gradually to the retaining pile and the soil behind the pile. The main factors affecting prestress loss of anchor cable are cable retraction, creep of soil mass and rheological deformation of rock mass caused by sudden unloading. Finally, the prestress loss rule of anchor cable under the action of GFRP waist beam, concrete waist beam and steel waist beam is compared and analyzed, and the overall loss rate is 6.89%, 14.74% and 16.84%, respectively. It shows that GFRP waist beam has absolute advantage in controlling the prestress loss of anchor cable. The research results can provide reference for the design of similar deep foundation pit engineering.