Abstract: The source range probe of RPN system in Daya Bay Nuclear Power Station is a boron-lined proportional counter. The middle range probe and the power range probe are boron-lined compensation ionization chambers. This paper introduces the relationship between different characteristic curves and aging of probes, and presents the way to identify the aging and malfunction of the neutron measurment probes in detail. For source range probe, if ΔC （aging extension of flat reigon in discrimative curve）＞60%, and the high voltage curve with aging trend by comparing with history curves, the probe has to be replaced. For middle range probe, the saturation curve of high voltage and electric current shall be drawn firstly, and then the coefficents P and V₀ are established. When the curve changes greatly or V₀ ＞ 70 V, it means that the probe is becoming aging, and it is necessary to draw the saturation curves every 3 months in order to monitor the aging.If the curve changes continuously or V₀ ＞140 V and P ＞ 6%,the probe has to be replaced. For power range probe,when the curve changes greatly or V₀ ＞ 30 V, it means that the probe is becoming aging, and it is recommended to draw the saturation curves every 3 months. If the curve changes continuously or V₀ ＞ 60 V and P ＞ 1.5%, the probe has to be replaced.