The effect of rotating speed on corner flow separation and its mechanism has been investigated by numerical simulation on an experimental annular cascades.The results show that the positive rotation of hub wall would reduce blockage in cascades.The mass flow rate of cascades is improved when the rotation speed increase.The 3-D hub corner separation can be removed by the rotation speed increasing.The detail analysis results show that the increasing of the leakage mass flow rate is the key reason for the corner separation removed.