Abstract: The shaft seal of reactor coolant pump (RCP) consists of three same hydrodynamic mechanical seals in series. It is the heart of RCP and its leakage directly determines the normal operation of the RCP. This paper introduces a new extruding deformation lapping method to manufacture the hydrodynamic mechanical seal. The stationary ring is deformed by using the extruding deformation tool and metallic gasket, and  nine waveform grooves are produced on the seal end face. The function test showed that the low-pressure (LP) leakage meets the design requirement of the shaft seal under the examination pressure. Meanwhile the impact examination under the saltation pressure showed that the liquid film between new hydrodynamic mechanical seal friction pair was intact, and no failure occurred on the seal. The operation of this hydrodynamic mechanical seal in the nuclear power plant shows that the operation performance agrees well with the function test results, and proves that this new hydrodynamic mechanical seal is with a high reliability in engineering application.