Abstract: The anti-siphon equipment is set in the primary sodium purification system of China Experimental Fast Reactor, which is used to passively reduce the sodium leakage when this system suffers any accident of the system pipeline breaks. From the point of view of bubble growing theory, the hydrodynamics analysis for the inlet of this equipment was performed. It is certified that the ability of the improved inlet, which includes depressurization and reducing the leak quantity of liquid, is better than the original one.