Francis turbine has the characteristics of high efficiency, compactable, reliable and able to adapt to a wide range of pressure head, therefore is one of the most widely used type of turbines. In general, large Francis turbine is generally applied in the range of 20-700 m head. Flow guided by the guide vanes go radially into the impeller, then changes its direction to the turbine main shaft, finally goes downstream along the tail pipe. Due to the transformation of direction within impeller, Francis turbine is sometimes called mixed flow turbine.