A hydrodynamic model of towed system is studied. The model of towed cable in this paper is based on the Ablow and Schechter method. A basic problem in the design of towed system is presented by the choice of Euler angles and tension at ending point of cable. This paper proposes a new way to design an ideal towed system. And a code is written to assist in designing the towed system. The governing equation is solved using a 4th-order Runger-Kutta numerical method for stable cable. The computed results with the code are close to the measured ones.