During the towing operations, towed vessels often slew. In order to study the relationship between towing slew angle and cable stress, the paper takes "DA DAN XIA" vessel as the example, under the stability of towed vessel, determines the relationship between towing slew angle and cable stress, and calculates the limit value of cable stress under the different slewing angle. Comparing with the cable stress on the tow vessel, the towing system can make a judgment for the safety of towing operations. The paper has practical significance for monitoring towing operations and ensuring the safety of towing.