Abstract: The cold or thermal neutron energy spectra on China Advanced Research Reactor (CARR) could be directly measured by neutron time of flight spectrometer. Spectrometer structure and selected parameters of its key components were introduced. The impact of chopper slit and flux limit slit on neutron counts and pulse width was analyzed. The formulas of neutron counts and pulse width which were dependent on neutron wavelength were acquired. According to neutron energy spectrum measurement requirement for high fluence rate neutron beam, low-sensitivity detector, detector flux limit slit and multi-channel scaler for data acquisition were selected. These would ensure that the count loss rate was less than 0.5%. Electronics framework of detection system was designed and the total resolution time was 22.15-29.46 μs.