To study the effect of anchor length on anchorage effect of weak rock masses in a deep tunnel, the indoor similar model tests were carried out on failure test of rock masses during the excavation opening. The variation characteristic on the failure, displacements and stress of the rock mass after excavation were analyzed comparatively under three conditions (without anchors, with short anchors and long anchors). In the loading test, the failure process of rock mass around the opening shows that the failure process of surrounding rock occurs first at the side wall, then the arch waist and the arch collapse. The surrounding rock in the arch roof after reinforcing rock bolts forms the effect of strengthening beam because of the reinforcement of rock bolts, which leads to the significant increase in the maximum settlement and failure load of the arch roof. The length of rock bolts need to pass through the plastic loosening zone of the arch roof. If the length of anchor rod is not enough to anchor the whole plastic loosening zone, there will be stratification between the anchored surrounding rock and the unanchored surrounding rock. Based on the theory of homogenization strength of rock mass, the short bolt mainly increases the effective support force of surrounding rock at shallow tunnel wall, thus improving the strength of surrounding rock, and the long bolt (cable) can regulate the stress in the elastic zone of deep surrounding rock. Therefore, the combination of the long bolt (cable) effectively regulates the stress state of surrounding rock.