Stress concentrations arising at hatch corners of the container ship with large opening is usually encountered. It is quite important for the designer to improve the stress concentration in the structural design phase. Recently, the type of hatch corner using key groove with circular hole has become a good remedy to deal with stress concentration problems. In this paper, Taguchi method, which is categorized into a fractional-factorial experiment, is adopted to find the optimal settings of parameters in the hatch corner of key groove with circular hole. Three examples of different typed hatch corners with key groove are taken for verification. It is found that results obtained from the Taguchi method are quite close to those from the full-factorial experiment and also, the former can even approach to 98% of the latter to the extreme. Therefore, Taguchi method can well improve stress concentration problems of the hatch corner in the large opening onboard and thus, it serves as an efficient tool for the design of the hatch corner.