The strength stratification of the rock and soil mass results in different ultimate bearing capacities for each segment of the anchor rod, leading to a reduction in the anchoring effect. A load-sharing composite anchor rod was designed for an in-situ test in a deep foundation pit where the strength of weathered mudstone was stratified due to the influence of underground water seepage. The results indicate that: (1)The bearing capacity of load-distributed composite anchor rods is more than 1.52 times higher than that of tension-only anchor rods of the same length, and is more than 1.13 times higher than that of load-dispersed composite anchor rods of the same length. Thus, the bearing capacity of the anchor rods has been further improved. (2)After immersion in water, the second interface shear strength of the anchor rods in moderately weathered mudstone is reduced by up to 66%, resulting in different ultimate bearing capacities of the anchor rod units. This affects the transfer and distribution of loads within the anchor rod sections. (3)The load distribution composite anchor rod ensures that each unit anchoring section carries a load close to its ultimate bearing capacity, achieving the goal of proportional distribution of anchor head loads based on the ultimate bearing capacity of each unit anchoring section. (4)By proportionally distributing the anchor head load, the structural ductility of the anchor rod is enhanced, effectively avoiding premature failure of the anchor rod at weak points. At the same time, this can also prevent the occurrence of cracks between the unit anchoring sections during the loading process. Therefore, the service life of the anchor rod is extended. (5)The load distribution composite anchor rod can provide internal support to the rock within the anchoring section, effectively improving the stability and load-bearing capacity of the surrounding rock mass. This helps prevent the occurrence of geological disasters such as rock burst and collapse, ensuring the safety and reliability of engineering structures. Additionally, the load distribution composite anchor rod can also effectively control the deformation and displacement of the surrounding rock, minimizing the impact on surrounding structures.