Abstract: A new simple calculation method was proposed to calculate the spectrum to dose function (G(E) function) of CdZnTe detector. The peak shape fitting function was used to feature the tailing of CdZnTe detector spectrum. The relationship between variable of peak shape fitting function and energy was derived from experiments. The Monte-Carlo method was used to simulate the ideal spectrum of CdZnTe detector. By convoluting the ideal spectrum and peak shape fitting function, the refined spectrum was derived, and it is in agreement with measurement spectrum. G(E) function of CdZnTe detector was calculated based on refined spectrum from simulation. The experiment result shows that ambient dose equivalent rate calculated via G(E) function is in good agreement with conventional real value of standard radiation field.