Abstract: Measurement and visualization of suction performance and cavitation development have been performed on a flat helical inducer with two blades.As the suction pressure is reduced,the balance of the cavity development on both blades may be destroyed.Alternate blade cavitation can occur,in which the cavity development evolves on one blade but weakens on the other.This makes the pump lift decrease quickly.Thus,the same investigation on four types of inducer impellers with different blade numbers and blade lengths have also been performed.The effects of the impeller geometrical parameters on the cavitation performance and occurrence of the alternate blade cavitation are found out and the mechanism is explored.