In order to increase the power output of tidal current energy, a new type of turbine blades and a Venturi-type duct were designed. Through in-door flume test, the roles of Venturi-type duct on increasing low velocity and rectifying oblique of the inflow were experimentally studied. The effects of different free stream drift angles, length-diameter ratios and area ratios of Venturi-type duct on the rotational speed of turbine were analyzed. Calculation formulas of the loads (thrust force, torque and radial force) exerted on the tidal current turbine were theoretically deduced. Changes in the relationship between the acting loads with free stream drift angles, length-diameter ratios and area ratios of the Venturi-type duct were analyzed combined with the experimental results. The results show that the Venturi-type duct can considerably increase the rotational speed of turbine, with the amplitude depending on the length-diameter ratio and area ratio of the guide duct. Under different drift angles, the maximum rotational speed occurs at the length-diameter ratios between 1.5 and 2.0, which means the guide duct should not be too long or too short. The rotational speed increases with the area ratio, and can reach the maximum value at the drift angle of 30°. The torque and radial force increase with the area ratio, but critical values exist for different length-diameter ratios and drift angles. The thrust force decreases with the drift angles. Compared with the case of free stream, the Venturi-type duct can not only increase the tidal current velocity, but also can rectify oblique inflow, thus enhancing the power inputted into the tidal current turbine.