Three horizontal axis tidal stream turbines (HATST) with winglets are proposed and investigated to enhance the energy conversion efficiency. Based on the conventional tidal turbine, three different winglets including trapezoid, triangle and blended types are equipped on the tip of the blade. The power coefficient, the thrust coefficient, the pressure distribution and the tip vortex are analyzed and compared to investigate the effect of the winglets on the hydrodynamic performance of HATST. Numerical simulation results show that the hydrodynamic model (Song et al., 2012) agrees well with the experimental test. At the optimal tip speed ratio (TSR = 5), the proposed tidal turbines could improve the energy conversion efficiency. The best hydrodynamic performance is demonstrated for the HATST with the triangle winglet, which reduces the intensity of the tip vortex and improves the energy conversion efficiency at all TSRs. The triangle tip turbine performs 4.34% increment in power coefficient and 3.97% increment in thrust coefficient at the optimal TSR.