Abstract: Nuclear measurement system is one of the most important measurement systems in nuclear power plant. By continuously monitoring the neutron flux signal in the reactor, the real-time power and power change of the reactor can be obtained. This can not only adjust the rise and fall of the control rod according to the power signal, but also prevent the phenomenon of overpower of the reactor. Moreover, it can provide the neutron fluence rate and change period to the reactor protection system to ensure its operation in a safe limit value range. During the transition from start-up to full operational capacity, there can be more than ten orders of magnitude change in neutron flux density. The traditional neutron flux measurement system in reactor generally uses several different detectors, each range corresponds to a relatively independent analog measurement system, which is not conducive to the continuity of measurement and control. If a single type of detector can be used for neutron flux measurement, it will have a unique simplification advantage for engineering design and operation maintenance. The fission ionization chamber has a wide dynamic measurement range, which can cover the neutron flux density change range of the reactor from start-up to full power operation, and has a high neutron/gamma retter capacity, which meets the requirements of wide range neutron measuring instrument. In order to match the three working modes of the fission ionization chamber and achieve the wider neutron flux measurement requirements of the fourth generation reactor, a wide range signal processing algorithm and a normalized connection algorithm between different operating modes were proposed. In order to verify the effectiveness of the proposed algorithm, the equivalent model of neutron signal output in the fission ionization chamber was constructed based on the numerical simulation method of Poisson process. The availability of the algorithm was verified through simulation experiments under different neutron fluence rates. The results demonstrate that the algorithm is capable of real-time neutron flux measurements at least 10¹⁰ cm⁻²·s⁻¹ using a single fission chamber, with a linear error of less than 1% when switching between different modes. The normalized fitting algorithm can accurately reflect the trend of variations in each pattern and effectively facilitates a seamless transition between different scales, so that the measured values can remain consistent over a broad range of scales, which is beneficial for the stable and rapid measurement of the reactors power increase cycle.