Abstract: In-Core Neutron Flux Measurement System is important system for nuclear power plant which directly monitors reactor core status. The availability of the system is related to the reliability and stability of the core component current amplification card. This paper researches the charge accumulation effect of ¹⁰³Rh-SPND. Charge shock modeling and calculating of micro-current measuring circuit under the most serious working circumstance are done, based on which the protecting scheme and detail design of measuring circuit are carried out. According to the results of laboratory test and reactor test, the current amplification card without protection occurs anticipated breakdown, while the current amplification card with protection achieves the charge shock protection. Furthermore, the characteristics of amplification card such as precision, response time and so on are also guaranteed. The test results of 2 units of ACP1000 proves that this protecting scheme can improve the availability of the micro-current measuring circuit well under different kinds of working condition.