Abstract: According to the prediction requirement of the measurement of fission product samples before and after the gas-solid separation, a simulation method for γ-ray spectrum measurement was established. With the way of modifying the independent yield database, all fission product activities before and after the gas-solid separation could be calculated. A universal calculation formula for the γ-ray peak areas was also deduced on the basic principle of gamma measurement by HPGe detector. Combining with above work, a simulation program was developed by employing Monte Carlo simulation code and PowerBuilder10.0 programming tool. The spectra of nondestructive analysis and gaseous fission product measurement were simulated. The results are consistent with those of experiments.