A 2D fully nonlinear wave-current numerical wave tank (NWT) based on BEM is investigated. In this paper, a new approach, a total velocity potential function is adopted to solve a wave-current interaction problem; meanwhile, the fully nonlinear free surface boundary condition is treated by using Mixed Eulerian-Lagrangian method (MEL). A linear and a high order wave-current theories are used as a feeding function separately to generate waves from input boundary, and assume the uniform current has existed in the wave tank before waves are generated. To dissipate the wave energy at the end of wall, a numerical damping zone is modified and deployed at the tank-end. A boundary element method with linear element scheme and the Runge-Kutta 4th order method are used to predict the water surface elevation varied with time. The simulated results show well agreement with other solutions in deep water as well as in intermediate water depths.