Tidal-stream turbines spend most of time in a shear flow environment, which leads to non-uniformity effect in stream vertical profile. To better understanding of such effect on tidal-stream turbine performance, the hydrodynamic performance and comparison between a bare turbine and a diffuser-augmented turbine under shear flow condition were numerically investigated. To closer to the real working environment of tidal-stream turbine, three major factors influence on hydrodynamic performance including flow shear rates, yaw angle and arrangement rule in array were discussed in detail. It is found that the different shear rate of flow will result in power and axis thrust slightly amplitude comparing with the uniform flow, and a diffuser turbine will further amplify this effect comparing with a bare turbine. The greater the yaw angle is, the more power and axis thrust is reduced. Additionally, there are “Advantageous Interaction” and “Disadvantage Interaction” in the wake effect on the energy extraction performance in the turbine array. The output power for each case is relatively concentrated at lower tip speed ratio (TSR) and divergent at higher TSR. Furthermore, each turbine in array operating at near 2D flow distance and relative deviation angle of 45° reaches its maximum CP.