Abstract: With the development of ultra-high voltage (UHV) transmission technology, the Hybrid Reactive Power Compensation (HRPC) which utilizes series compensation（SC） and step-controlled shunt reactor (SCSR) will be widely used. Therefore, the study on the influence of HRPC on the transient enclosure voltage (TEV) of gas isolated switchgear (GIS) is significant. Based on simplified equivalent model of grounding GIS, the simulation analysis of the TEV waveform and frequency characteristics before and after the installation of HRPC has been carried out. In both conditions of grounding that HRPC and GIS are connected to same and different grounding grids, the relationship between the amplitude of the TEV main frequency oscillation and the installation position of the HRPC have been analyzed, Besides, the influence of the SCSR entrance capacitor and the SC capacitor on the corresponding amplitude of the TEV main frequency is analyzed as well. The results show that, compared with the case of non HRPC, the TEV oscillation of the GIS is more severe after the installation of HRPC, the peak value of TEV does not change notably, and the amplitude of the TEV main frequency has been greatly improved. With the increase of the distance between HRPC and GIS, the amplitude of the TEV main frequency decreases. The TEV main frequency amplitude increases with the equivalent capacitance of SCSR, and does not change with the variation of the earth capacitance.