In this paper, the geological investigation and design technologies for underwater highway tunnel are summarized; the characteristics of design and construction of drilling and blasting tunnel, shield tunnel, immersed tunnel and cofferdambuilt tunnel are proposed. The author suggests that the investigation results of underwater tunnel have to meet the requirements of design and construction of the tunnel; the geological investigation quality is decided by investigation scheme, method and results; the rational geological investigation scheme and relative investigation works are the keys to geological investigation and the engineering construction. The rational geological investigation methods and depths for underwater tunnels under different geological conditions are proposed. The results can provide reference for quality and safety of construction of underwater tunnels in the future.