Abstract: The research of Segmented Gamma Scanning(SGS) technique is mainly focused on two aspects: self-absorption correction of waste drum and efficiency calibration of the system. For the purpose of self-absorption correction, it is necessary to calculate the scanning efficiency. In this paper, a mathematical model was established for the correction, which was based on the spatial distribution of radioactive waste barrels, collimators and HPGe detectors in SGS detection systems. In addition, calculation of the detection efficiency of midpoint sources (Cs-137) in low and intermediate level radioactive waste steel drum was managed. Then the calculation corresponding to efficiency function based on MCNP method was operated as well. The results of the two methods were compared with the numerical calculations. It was found that the results from numerical calculation was usually larger than that from MCNP simulation and the maximum relative error reached 143.26% whereas the average error was 37.15%. After correction the maximum error was reduced down to 17.22% and the average value was 4.54%, which indicates that the model is scientific for the temporary storage, transportation and final disposal of the waste bucket.