The underwater operations of two cables are simulated and analyzed by Matlab together with the simulation analysis method of the rigid body dynamics based on the finite element method (FEM) that has been widely used in the hull structural design. The obtained variation of the cable posture with time can determine whether the double cable will interfere with each other underwater. It firstly analyzes the influence of the ship motion on the cable launching point, and then builds the dynamical model for the cables underwater. Finally, the cable posture underwater is obtained through the simulation.