The influence of the shape and the size of the moonpool on the vulnerability criteria assessment of the parametric roll and the excessive acceleration in the second generation stability has been analyzed for a drillship. This article considers the drillship with three moonpools of different opening shapes and different sizes to verify and analyze whether the drillship meets the second generation intact stability criteria under development. The analysis results indicate that the variation in the shape and size of the moonpool can affect the parameters of the vulnerability criteria of the parametric roll and the excessive acceleration for the drillship. The drillship with the moonpool of the shapes and sizes considered in this study can meet the criteria requirements. It can provide reference for the design of the drillship's moonpool.