Abstract: During the operation, maintenance, and eventual decommissioning of nuclear power plants, a significant amount of low and intermediate-level radioactive waste is generated. The measurement and management of this waste require precise radiation detection methods. High-purity germanium (HPGe) detectors are commonly employed in this context due to their superior characteristics, including high energy resolution, high detection efficiency, and a broad detection range. However, to ensure the optimal performance of HPGe detectors, it is crucial to configure them with accurate parameters and an appropriate structural design. One of the key challenges in using HPGe detectors lies in the time-consuming nature of the current calibration methods. These calibration processes are essential for achieving accurate measurements but often take up a considerable amount of time. As a result, there is a pressing need for the development of new calibration techniques that can significantly reduce the time required without sacrificing accuracy. In this study, the calibration efficiency of HPGe detectors used specifically for measuring low and intermediate-level radioactive waste drums was improved. The study primarily focused on addressing the limitations of current calibration methods by proposing more efficient alternatives. To achieve this, the Monte Carlo simulation method was employed to model the behavior of the detectors under various conditions, including different crystal diameters, varying distances between the detector and the waste drum, and different eccentricities. After these simulations, the detection efficiencies for various conditions were compared to identify how crystal diameter impacts detection efficiency. A key finding is that the distance between the detector and the waste drum, as well as the eccentricity, has little effect on the detection efficiency ratio between different crystal diameters. Further analysis reveals that the ratio of detection efficiency for crystals of different diameters, when compared to a standard crystal size, increases in an approximately linear manner with the crystal diameter. Based on these observations, a set of correction coefficients was developed and applied to predict the detection efficiency for crystals of other diameters. Upon comparing the simulated detection efficiencies across various conditions with those obtained using the correction coefficients, the relative error is found to be within 5.5%, indicating high accuracy. Moreover, no significant correlation is observed between changes in detection efficiency and variations in eccentricity or distance. This study provides a practical method for correcting detection efficiency errors caused by variations in crystal diameter, offering a more efficient approach to calibrating HPGe detectors for radioactive waste measurements.