Abstract: To capture the bidirectional tidal current energy effectively,a novel swept-back horizontal-axis tidal stream turbine based on symmetrical airfoils was designed and its hydrodynamic performance was discussed. According to the lift-drag characteristics of the symmetrical airfoils and the different spanwise angle of attack,the backward swept blade was optimized by a variable section design,and the thrust and captured energy of the rotor with different offset blades were analyzed based on the Buhl model. Through 3D modeling and flume experiment,the load and captured energy of the rotor model are presented. The experiment results show that at the same TSR,the thrust of the turbine with backward swept offset of 10% and 15% is reduced by 4% and 13.3%,respectively,compared with the turbine with 5% offset. Meanwhile,the energy harvesting efficiency is reduced by 3.8% and 11.1%,respectively. In contrast,the thrust ratio has a greater reduction than the energy harvesting coefficient. The variation trends of the experimental results are consistent with that of the theoretical analysis,but the reduction range is higher than that of the latter. In addition,the corresponding energy harvesting efficiency of the turbine under the three sweep offsets decreases by 18%,14%,and 6% with the increase of the pitch angle,the trend of which is the same as that of the field test of the 300 k W prototype.