Abstract: In order to solve the problem of self-absorption correction in γ-ray efficiency calibration of fission gas nuclide, the parameters about source container, detector and source matrix etc. were described, and Monte-Carlo model and program of efficiency computation for HPGe detector were established according to experiment layout. The efficiency of fission gas nuclides was calculated in the different source matrices, and the corresponding self-absorption coefficients were obtained. The reliability of the model was validated by the experiment data.