<p>The full-face tunnel boring machines (TBMs) serve as core equipment in tunnel engineering, where the synergistic rock-breaking mechanism and efficiency of the disc cutter system being key scientific issues determining tunneling performance. Given that the synergistic effect and efficiency evolution of the double disc cutters system under multi-mode loading remain poorly understood, this study systematically reveals the physical mechanisms and efficiency evolution characteristics of rock fragmentation by double disc cutters under multi-mode loading through a combined approach of theoretical modeling, indentation testing and numerical simulation. Based on the crack propagation distribution characteristics, theoretical models for the normal and rolling forces of the disc cutter were established. Digital image correlation (DIC) technology was used to conduct in-situ observations of double disc cutters indentation tests, and a numerical model capable of reproducing the dynamic rock-breaking process was constructed. This study systematically clarified the dynamic rock-breaking mechanism and rock damage evolution of double disc cutters, and quantitatively analyzed the intrinsic mechanisms of cutter spacing on rock failure modes and rock-breaking efficiency. The results showed that the distribution of rock fracture areas under different rock-breaking modes differed significantly: The synergistic mode exhibited concentrated fragmentation between disc cutters, while the independent mode was mainly confined to beneath and on both sides of a single cutter. Stress field interference effects (simultaneous loading) and free surface effects (sequential loading) are the key physical mechanisms that dominate the efficiency evolution. As the cutter spacing increased, the rock-breaking force exhibited a non-monotonic trend, initially increasing before stabilizing. The rock-breaking volume and area exhibited an initial increase, followed by a decrease, and eventual stabilization. The specific energy exhibited an opposite “U”-shaped evolution pattern, verifying the existence of optimal cutter spacing. The efficiency evaluation further demonstrated that when the ratio of cutter spacing to penetration depth (S/P) was approximately 12 (simultaneous loading) and 14 (sequential loading), the system achieved the lowest specific energy and the optimal rock-breaking efficiency. This study provides important theoretical guidance for optimizing the TBM cutterhead layout and controlling tunneling parameters.</p>