Abstract: Based on the compound structural characteristics of tunnel surrounding rock, the principle of anchoring system synergistic effect is illuminated, and a corresponding mechanical model is established. The whole process of the interaction between an anchoring system and surrounding rock is solved. Tunnel surrounding rock is a composite of the internal instable surrounding rock and the external surrounding rock with strong load-bearing capacity. Rockbolt forms ‘a surrounding rock massive structure’ through a ‘composite beam’ or ‘compression arch’ effect. This structure is suspended to external stable surrounding rock by an anchor, and the core of synergy is to mobilize external surrounding rock bearing. The sensitivity analysis of bolt parameter indicates that increasing the length, prestress and density of a rockbolt can significantly reduce the deformation of surrounding rock, while its diameter has little effect on surrounding rock deformation. Calculations show that:appropriate length lies in passing through the internal surrounding rock and stretching into the first structure layer of external surrounding rock, and the reasonable values of bolt parameters have an obvious matching effect. The synergistic effect essence of an anchoring system is its deformation coordination and load rational distribution. The parameters of rockbolt and cable matching each other can give a full play to the assembly efficiency and improve the stability of surrounding rock. Taking the surrounding rock deformation and support synergy degree as evaluation indices, the synergistic effect evaluation system of a tunnel anchorage system is put forward, then the determination method of tunnel anchorage parameters is proposed based on anchoring system synergy. The research results give a comprehensive understanding of synergistic effect of a tunnel anchorage system, which can provide a theoretical basis for the quantitative design of the anchoring system in tunnel and underground engineering.