Deep seafloor extremely soft cohesive sediment is completely different from land surface soils, which need high requirements for structure design and mobility performance of the seafloor operated machine. According to the physical and mechanical properties of the seafloor sediment, laboratory simulated sediment is prepared. Based on the theory of terramechanics, mechanics experiments on the simulated tracks and simulated sediment interactions are performed. The normal pressure-sinkage and horizontal shear stress-shear displacement mathematical relationships are obtained. According to the detailed structure design parameters of the deep seafloor tracked miner, its multi-body dynamic model is built by the dynamic modeling and simulation code RecurDyn/Track. Application of the mechanics relationships of the seafloor sediment obtained from experiments, user-written subroutines are compiled with C language. Based on the secondary development for RecurDyn/Track, the development of the deep seafloor sediment mechanics model in the RecurDyn/Track is realized. Various dynamic simulations of the tracked miner on the seafloor special sediment are carried out. The mobility performance of the miner are analyzed and evaluated, which lay the foundations for the structure design optimization, mobility performance evaluation and moving control of the practical deep seafloor tracked miner.