Abstract: For APG system in Ling’ao nuclear power station,ammonia-type operation mode is expected to replace the hydrogen-type mode.The analysis,evaluation and verification are performed for the feasibility of this replacement.The results of verification indicate that ammonia-type operation mode could extend the life of demineralizers and reduce the procurement cost of resin and the disposal cost of waste resin.Though the water treatment effectiveness of the demineralizers would be reduced to some extent,but still within the range required by the code.It is recommended to replace the current hydrogen-type cation resin operation mode and the corresponding measurement instrumentation.