Based on the partial discharge(PD) combined detection platform in the laboratory, the experiments under the four typical defects are performed, and the PD optical signals and PD electrical signals are obtained. The relationship between the two types of PD signals and the charge quantity is analyzed. According to the actual influence factors in the field test, the results were corrected. The relationship between UHF signal and charge quantity under different pressures are revised, the relationship between optical method and charge quantity under different size of insulation defects are also revised. A correction formula for the effect of air pressure on the UHF signal is obtained. When the pressure in the simulated cavity is 3 bar, the correction value is compared with the measured value. Except for the free metal particle defect (relative error is 14.4%), the relative error of other defects is less than 5%. A correction formula for the effect of different defect sizes on the optical signal is obtained, and the minimum size of each type of defect is selected to calculate the correction value. Comparing with the measured values, it is found that the relative errors of other defects except the free metal particle defects are less than 10%, which verifies the reliability of the correction result.