This paper investigates into the type of growth environment required for the tropical seagrass of Okinawa sea area. Due to the open geographical location of Okinawa sea area, the tropical seagrass beds in this area are often subject to typhoon waves and strong currents. These physical factors are known to alter the seafloor structure, and confirmed that it leads to the disappearance of the seagrass beds and limitation of their growth. In order to determine the ideal growth environment for the seagrass, a new parameter, which measures the depth of seafloor sand layer was introduced.