A helideck is a very valuable offshore structure for the take-off and landing of a helicopter. In order to design a helideck, the design parameters and various loads defined by the regulations related to the design of a helideck should be applied. In this study, a risk analysis was performed based on the helicopter accidents for seven years, and the frequency and possible reasons for accidents involving helidecks were investigated. In addition, a finite element analysis of a steel helideck mounted on the upper deck of a ship (shuttle tanker) was performed with the load that should be considered when designing a helideck. Based on the results, a parametric study of helideck was carried out by applying a variety of design parameters, and an improved helideck design was presented. This improved helideck reduced the steel used by up to 24% compared to the initial helideck design, and the results of a finite element analysis were analyzed and compared with those of the initial analysis.