This article presents a numerical approach to estimate power output from a tidal current turbine farm with first-order approximation of hydrodynamic interactions between multiple turbines. An example study is conducted by using this approach to design a tidal current turbine farm in an ideal site with the objective of maximizing the power output of the farm by optimizing the turbine distribution in the site. The results suggest that the maximum power output of a farm can be significantly improved with the utilization of the constructive hydrodynamic interaction between turbines. Limitation of this approach is discussed at the end.