To reduce the structural failure risk of net cages under extreme sea conditions, this study analysed the yield phenomenon under mooring constraints and excessive or long-term wave loads. The floating collar deforms by shear when a twisted 1 m for the 8-point type and 5 m for the four point type. The structural strength in the Z-vertical direction is one-fifth of that in the X-horizontal direction. The maximum deformation is mainly on the two ends of the cap ned pipes. The critical points of the guardrail may reach the yield stress when the wave height is 1.1 m, while the height of the floating pipe is 5 m. The float can be damaged more easily when there is torsion or shear deformation caused by irregular waves. The results provide guidelines for the optimised structural design of net cages, which by increasing the number of mooring points and cap neds as well as reducing the welding points and structural mutation points, can improve the ultimate bearing capacity and fatigue reliability of the cage float.