In order to better apply the NaI scintillation spectrometer to bremsstrahlung measurements, the energy response function of a NaI detector spectrometer system is studied by using 137Cs and 60Co sources based on Monte Carlo N particle transport code (MCNP) process. Simulated and measured almighty peak efficiency are in good agreement. An energy response matrix (ERM) is obtained by simulating photons with a certain energy incident on the NaI crystal in MCNP process, through deconvoluting the detected spectrum of NaI using the ERM, and the results of the deconvolution accord well with those from the original spectrum. Furthermore, the NaI detector is used to preliminarily detect its response to bremsstrahlung generated by high intensity electrons bombarding a target of 1.5 mm thickness.