Variable angle adjustment is an effective measure which is usually used to widen the operating range of axialflow pump. In order to ensure the adjustability of blade placement angle in bidirectional axialflow pump, a certain clearance will be reserved between blade and hub during structure design of the impeller. The hub clearance will change with the adjustment of the blade installation angle. According to engineering experience, inappropriate size of the hub clearance will significantly affect the hydraulic performance of the axial flow pump. Therefore, the effects of hub clearance on hydraulic performance of bidirectional axialflow pump should be analyzed. Five clearance radii of impeller hub (0mm, 1mm, 3mm, 5mm and 8mm) were designed. Threedimensional Reynoldsaveraged Navier-Stokes equations was solved by CFX to predict external characteristics of bidirectional axialflow pump. The results were verified by experimental data. It was shown that when hub clearance was too large, head and torque of pump were decreased significantly both under forward and reverse condition. The decline of pump efficiency due to increase of hub clearance under large flowrate was more obvious. And the maximum relative decline ratios of pump efficiency under forward and reverse condition were 5.72 percentage points and 3.48 percentage points respectively. In impeller passage, the leakage rate of hub clearance was increased with the increase of clearance radius. Near impeller hub, the axial velocity and circulation of impeller outlet declined remarkable with the increase of clearance radius. This result can provide useful suggestion to structural design of bidirectional axialflow pump.