Partial wear is one of the fatal abnormal wears, which may pose a threat to the cutterhead or even the driving system. Considering the randomness of partial wear, the real-time detection and early warning of partial-wear states are very important, but it requires a deep understanding of the mechanism and characteristics of the interaction between the partial-worn cutter and rock. In this study, rock-cutting experiments are conducted on a cutter under partial wear via multifunctional cutter test machine. The key dynamic parameters of the partial-worn cutter (e.g., loading history during rock cutting) are analyzed. The influence of partial wear on cutter-rock contact behavior is examined with a particle flow discrete element model. The results show that after partial wear, the contact area of the cutter can be divided into two parts: an arc region and a linear region. Reduction in the projected area of the arc region decreases the normal force of the cutter. The appearance of the linear region and changes in the friction type between the cutter and rock from rolling to sliding increase the tangential force. The partial-worn cutter still has rock-breaking ability, but the linear contact region prolongs the working time of the cutter and generates more rock powder, ultimately increasing its rock-cutting specific energy. The results of this work reveal changes in rock-cutting characteristics of partial-worn cutters, providing workable theoretical support for the detection and early warning of partial wear in cutters.