Underwater diamond wire sawing machine is a kind of clean and environmentally friendly machinery that is developed in recent years. Its structure and working principle are introduced. The force of single bead cutting process was analyzed，aiming at the pipe cutting, the mechanical model was established. Through the analysis of the model, the calculation formula of the pressure on the bead in the process of wire saw cutting was obtained. In order to make the bead rope saw in the cutting process achieve a certain degree of circumferential rotation, a certain torque might be applied to the bead rope saw in advance, and the corresponding calculation formula was obtained. The underwater wire sawing machine test system was set up, the characteristics of bead wire saw in cutting process were experimentally studied. The results show that the experimental results are in good agreement with the corresponding theory, which provide a basis for further rational optimization of cutting parameters of underwater wire sawing machine.