Abstract: Anti-floating anchors are widely applied in the anti-floating design of underground structures, and the group anchor effect is a critical factor affecting the overall bearing performance of anchorage systems. Traditional finite element methods struggle to accurately capture the meso-mechanical behavior at the anchor-soil interface, whereas the Discrete Element Method (DEM) can reveal the interaction mechanism between anchors and soil at the particle scale. In this paper, a numerical model of anti-floating group anchors is established based on the Particle Flow Code (PFC). The parallel bond model is adopted to simulate the mechanical response of the anchor-soil interface, and the influence laws of anchor spacing and anchorage length on the group anchor effect coefficient are systematically investigated. The results show that the group anchor effect coefficient increases nonlinearly with the rise of anchor spacing and gradually approaches 1.0; increasing the anchorage length can mitigate the group anchor effect to a certain extent, yet the improvement exhibits a diminishing trend. The reliability of the discrete element model is verified through comparison with field group anchor test data, and an empirical formula for the group anchor effect reduction coefficient applicable to engineering design is fitted. Furthermore, the macroscopic failure modes and meso-evolution mechanisms of group anchor failure are revealed from the perspectives of meso force chain evolution and particle displacement field, which provides a theoretical reference for the optimization of design spacing of group anchors.