Neutron flux monitor (NFM) as an important diagnostic sub-system in ITER (in-ternational thermonuclear experimental reactor) provides a global neutron source intensity,fusionpower and neutron flux in real time.Three types of neutron flux monitor assemblies with differentsensitivities and shielding materials have been designed.Through MCNP (Mante-Carlo neutralparticle transport code) calculations,this extended system of NFM can detect the neutron flux ina range of 10~4 n/(cm~2.s) to 10~(14) n/(cm~2.s).It is capable of providing accurate neutron yield mea-surements for all operational modes encountered in the ITER experiments including the in-situcalibration.Combining both the counting mode and Campbelling (MSV;Mean Square Voltage)mode in the signal processing units,the requirement of the dynamic range (10~7) for these NFMsand time resolution (1 ms) can be met.Based on a uncertainty analysis,the estimated abso-lute measurement accuracies of the total fusion neutron yield can reach the required 10% level inboth the early stage of the DD-phase and the full power DT operation mode.In the advancedDD-phase,the absolute measurement accuracy would be better than 20%. Neutron flux monitor (NFM) as an important diagnostic sub-system in ITER (in-ternational thermonuclear experimental reactor) provides a global neutron source intensity, fusionpower and neutron flux in real time. Three types of neutron flux monitor assemblies with different seisms and shielding materials have been designed.Through MCNP (Mante-Carlo neutral particle transport code) calculations, this extended system of NFM can detect the neutron flux ina range of 10 ~ 4 n / (cm ~ 2.s) to 10 ~ (14) n / ( cm ~ 2.s). At is capable of providing accurate neutron yield mea-surements for all operational modes encountered in the ITER experiments including the in-situcalibration. Combining both the counting mode and Campbelling (MSV; Mean Square Voltage) mode in the signal processing units, the requirement of the dynamic range (10-7) for these NFMs and time resolution (1 ms) can be met. Based on a uncertainty analysis, the estimated abso-lute measurement accuracies of the total fusion neutron yield can reach the re quired 10% level inboth the early stage of the DD-phase and the full power DT operation mode. in the advancedDD-phase, the absolute measurement accuracy would be better than 20%.