The invention discloses a device and a method for [gamma] and neutron double ray power spectrum measurement. The [gamma]-ray signal and the neutron signal are distinguished by particle discrimination by using the feature of a scintillation crystal being sensitive to the [gamma]-ray and the neutron at the same time. The pulse amplitudes of the two signals are analyzed respectively to obtain the [gamma]-ray deposition spectrum and the neutron deposition spectrum. The [gamma]-ray has a peak response in the scintillation crystal, and the [gamma]-ray spectrum is the measured [gamma]-ray power spectrum. The neutron is continuously responsive in the scintillation crystal. The neutron power spectrum is solved by the least squares of the response matrix and the neutron deposition spectrum of a single energy neutron. Finally, by analyzing the energy spectrum data, the key nuclide is identified and the content thereof is calculated, and the [gamma] dose and the neutron dose are calculated. The portability of the instrument for mixed radiation field measurement is effectively improved and the mutual interference between the [gamma]-ray and the neutron is avoided.