The minimum rock cover is one of the most important factors determining the safety and cost of subsea tunnels .There are seven main influence factors and four methods determining the rock covers of subsea tunnels. Unfortunately, whether in Norwegian experience method (NEM), Numerical method (NM), Japanese experience method (JEM) or in mining under water experience method (MUWEM), these factors are considered separately in the study. The synergies reflecting the preferred primary or minor importance between the factors are not fully considered. The group AHP method (GAHPM) was put forward to solve the problem. GAHP is an optimization technology, where choosing suitable weights are the most importance. Adopting the advantage of AHP and avoiding the disadvantage at the same time, it can fully reflect the importance of each factor in determining the ultimately thickness of rock covers. In this paper, firstly, we construct the hierarchy and pair-wise comparison matrix. Secondly, determine weights of the experts. Thirdly, check the consistency of the judgment matrix. Ultimately, we obtain the ultimate minimum rock cover of the subsea tunnel by the product of initial selectable thicknesses and weights.