Abstract: The excore neutron detection technique for the power measurement in an accelerator driven sub-critical system has been studied in this work. Firstly, the physical process of proton beam bombarding spallation target, and the neutron transport process in the subcritical reactor driven in the ADS system have been simulated with FLUKA and OpenMC. Based on the calculated energy distribution of the excore neutrons, the neutron detection systems suit for both the high-power range (HR) and low-power range (LR) in the ADS system have been developed respctively. The uncompensated boron-coated ionization chamber for the power range measurement in pressurized water reactors can be used for the neutron detection of the HR in the ADS system, while the γ-compensated boron-coated ionization chamber for the intermediate range measurement in pressurized water reactors can be used for the neutron detection of the LR in the ADS system. In addition, in order to measure ultra-low neutron fluence rate, the γ-compensated fission chamber can be used for the neutron detection of the LR. It is found in the study that if the polyethylene with a thickness of 4 cm is placed in front of the neutron detectors for the LR, the detection efficiency can increase by 10 times. Finally, the signal processing technology of neutron detectors has been studied through the simulations with Garfield. The signal processing technology of current mode can be used in both the boron-coated ionization chamber and the fission chamber. The detectable neutron fluence rate ranges from 10⁵ to 10¹¹ n/(cm²·s). The fission ionization chamber with the pulse mode can detect neutron fluence rate of 100 n/(cm²·s) or more.