Tunnel boring machine (TBM) is widely used in tunnel construction. The boring efficiency is mainly affected by the cutter arrangement and construction parameters, in which the cutter spacing is designed to be reasonable and whether the penetration degree is set to be appropriate are the most important two aspects impacting the efficiency of rock breaking. As a direct product of rock breaking by cutter, rock ballast can provide comprehensive and intuitive feedback on the rock-breaking efficiency of TBM. The correlation mechanism between ballast particle size distribution and rock breaking efficiency is revealed by analyzing the rock chip morphology of granite cutting test. Based on the theory of characteristic particle size to predict the optimal penetration, it is verified by multiple working conditions that: The optimal penetration is 2.0 mm for cutter spacing of 60~70 mm, 2.5 mm for cutter spacing of 80 mm, and 3.0 mm for cutter spacing of 90~100 mm, and the characteristic particle size of the rock chips reaches the peak when the ratio of the cutter spacing to the penetration is in the range of 30~40, corresponding to the optimal efficiency of rock-breaking. It can dynamically optimize and adjust the combination of boring parameters according to the real-time monitoring of the characteristics of the rock chip particle size, and realize the scientific matching of the knife spacing and penetration.