With the wide application of large-diameter tunnel engineering in complex stratum, the rock-breaking efficiency of shield cutter has become a key factor restricting the tunneling efficiency. Most of the existing studies focus on the force and spacing optimization of single-edged disc cutters, and the systematic analysis of the coupling mechanism between blade spacing and lithology of double-edged disc cutters is still lacking. In this paper, based on the discrete element method, the rock breaking process of double-edged hobs with different blade spacing in soft rock to extremely hard rock is simulated, and the stress response, crack propagation and specific energy change are analyzed. The results show that the large spacing in soft rock is helpful to realize fracture penetration and reduce specific energy. There is an optimal spacing interval of 70-80 mm in medium-hard rock. The small spacing in hard rock can enhance the stress concentration effect, while the spacing effect in extremely hard rock is significantly weakened, and the damage is dominated by crushing under the blade. This study reveals the coupling law between blade spacing and rock strength, which provides a theoretical basis and engineering reference for the design of shield cutterhead and the dynamic optimization of tunneling parameters in complex stratum.