With the worldwide trend of controlling the utilization fossil fuels inducing global climate change, many efforts will have to be made on securing stable supply of the energy due to UNFCCC. Tidal currents are a concentrated form of gravitational energy. Tidal current resource is significant, but limited locations. Technical and economic feasibility demonstration is the next needed step in the technology development process. So, we investigated overview of tidal in-stream energy in the sea near Wando, and then analytically estimated tidal energy resources and annual energy output of TECS arrays.