Abstract: NaI spectrometer is commonly used in nuclear emergency monitoring to realize dose rate monitoring and γ radionuclide identification. This paper introduces the calibration of the direct conversion of energy spectrum to dose for a 3″×3″ NaI spectrometer by using the G(E) function method. The standard energy spectrum data under different energies are obtained by using ¹⁵²Eu, ¹³³Ba, ²⁴¹Am, ¹³⁷Cs, ⁶⁰Co and other standard point sources, and the energy spectrum data under other energies are simulated and calculated by Geant4 program, and the conversion of energy spectrum information to air absorption dose rate is realized. The analysis results show that in a certain dose rate range, the G(E) function method can be used to convert the energy spectrum information to dose rate, and the results are acceptable and meet the requirements of emergency monitoring.