In this study, the performance of a contra rotating vertical-axis tidal-current turbine was investigated. The incompressible unsteady Reynolds-averaged Navier-Stokes (U-RANS) equations were solved via two-dimensional (2D) numerical simulation using ANSYS Fluent computational fluid dynamics (CFD) code. An algorithm known as SIMPLE from the CFD code was used to calculate the pressure-velocity coupling and second-order finite-volume discretization for all the transport equations. The base turbine model was validated using the available experimental data. Three given scenarios for the contra rotating turbine were modeled. The contra rotating turbine performs better in a low tip speed ratio (TSR) than in a high TSR operation. In a high TSR operation, the contra rotating turbine inefficiently operates, surviving to rotate in the chaotic flow distribution. Thus, it is recommended to use contra rotating turbine as a part of new design to increase the performance of a vertical-axis tidal-current turbine with a lower TSR.