In order to solve the problem that the average efficiency of power generation equipment decreases in a tidal current cycle due to the influence of blade airfoil, and to improve the total output power of the generation equipment, a bidirectional diversion device that can convert the two-way flow of tidal current into one-way flow was studied. First, the mathematical model of the output power of a generation device was established, and the influence of the fillet radius on the internal flow field, resistance coefficient k, flow rate ratio of the bidirectional diversion device and the output power of the turbine were studied by numerical analysis. Then, the underwater test was carried out to test the actual performance of the bidirectional diversion device. The results showed that when R<1.4 l, the increase of the radius of the transition fillet was conducive to reducing the flow resistance loss, improving the velocity distribution and enhancing the performance of the bidirectional diversion device. Under the same load, when the current velocity was 1 m / s, the average electric power of the load increased by 79% compared with that of bare blade. It indicates that the installation of bidirectional diversion device can avoid the negative effect of the reversed flow of tidal current and significantly improve the average output power of equipment in a tidal current cycle.