In tidal two-way contra-rotating units, significant differences in performance often occur when arranging the front and rear impellers, which requires an optimized design of the impellers. To solve this problem, by reducing the blade inlet and outlet angles, the impact of different blade angles on the performance of two-way pump−turbines and the internal flow was explored, and the effects of the blade inlet angle of the impellers on the performance of the counter-rotating pump were obtained. Afterward, the streamline and vorticity of the two-stage impeller at different angles were analyzed. The results show that different blade angles will have a certain impact on the internal flow of the two-way pump−turbine. Different blade outlet angles have a significant impact. The variation in different inlet blade angles is not significant for the vorticity changes in the front impeller and rear impeller. In addition, changes in the outlet blade angle will have an impact on the location of LE impact water of the rear impeller, which in turn affects the contours of vorticity of the rear impeller near LE, which also means that the vorticity in this area is mainly dominated by the vortex stretching term.