Abstract: Umbilical is one of the most important equipment for the marine oil and gas resources development.Umbilicals are generally composed of multiple units twisted and wound,such as hydraulic,chemical injection,and power cables. The position of internal units in the umbilicals are different,and the fatigue life of the unit is inconsistent.Factors such as mutual friction,compression,and structural dimensions between the units have a certain impact on the fatigue life of umbilical tubes. Therefore,this article research on cross-sectional optimization design method based on the variables such as relative position and geometric position relationships of tubes,the optimization design goal is the fatigue life of umbilical tubes. Develop cross-sectional design software by combining unit position variables and the fatigue life of the tube,a cross-sectional optimization design method for umbilical based on maximizing fatigue life of the tube is proposed.