In this research, the mechanical characteristic parameters of the seabed massive sulfide (SMS) are obtained quantitatively using laboratory uniaxial compression strength (UCS) test and triaxial compression strength (TCS) test. A three-dimensional discrete element (DEM) model of the SMS is developed in the EDEM simulation environment and are then validated by numerically simulating the laboratory UCS and indirect tensile strength (Brazilian disc) tests. A new counter-rotating pick-type drum cutter for excavating the SMS is proposed, and a corresponding DEM model for the excavation process is established. Numerical simulations for the new counter-rotating cutter and a traditional single-rotating cutter are conducted, and the cutter forces in three orthogonal directions and the torques are obtained and compared. By integrating the new counter-rotating cutter, a three-dimensional multi-rigid-body dynamic model of a SMS mining machine is developed in the RecurDyn simulation environment, and simulations are conducted to evaluate its trafficability and mobility performance under the effect of the excavating cutter on the seabed complex terrain. This research can provide valuable and effective modelling methods for seabed mineral excavation process simulation, mining tool optimization and design and mining machine performance evaluation.