Abstract: To figure out the problem of neutron energy spectrum measurement in pulsed fission, a numerical iteration method for neutron energy spectrum based on Bayesian theory was established in this paper. The spatial transport, material attenuation and detector sensitivity were analyzed. In the proposed method, the broadened time-of-flight spectrum was regarded as the probability distribution function of off-shell time spectrum at different measuring points. The signal intensity distribution of pulsed neutron at different measuring points is the convolution of off-shell time spectrum and the broadened time-of-flight spectrum. The impact factor of the conversion process, such as material attenuation and detector sensitivity, on neutron energy spectrum was disposed, respectively. The influences of several factors, including neutron energy spectrum attenuation by channel materials and non-linear detector sensitivity, on the unfolding of the neutron energy spectrum were eliminated. The result shows that the ideal pulsed fission neutron spectrum can be obtained after the numerical treatment for the neutron waveforms with the distance of 5 m and 10 m from the radiation source, respectively. When taking into consideration of the effect of the response function for the transmission system to the neutron waveform, the relative ideal neutron spectrum can still be obtained.