For the structure of the drilling vessel moon-pool area structure, the simplified method of stiffener with equivalent cross-sectional area of panel laid into web is adopted.Considering the nonlinear factors, the ultimate bearing capacity of the moon-pool structure under vertical bending moment, horizontal bending moment and torsion condition is researched. According to the failure mode under the limit state, the local strengthening measures are proposed for the moon-pool structure and the comparative analysis is carried out. The study shows that: the location prone to failure is located at the partial structure in the upper deck structure of section 2; when the cabin of moon-pool area bears the ultimate vertical bending moment load, it is more dangerous in the mid-sag condition; to enhance the ultimate strength of the mid-cabin section under the vertical moment load, it is necessary to locally strengthen the upper deck and the ship's floor structure.