The fast linear transformer drive (FLTD) is a new type of pulse power source developing rapidly in recent years. It usually adopts multi-gap gas switch (MGS) as its primary switch. The corona discharge for voltage balance was proposed to improve the switch breakdown performance. However, great difference of corona discharge in different gases may exist and affect the performance of MGSs. In this paper, the effects of needle electrode in air on single-gap corona discharge characteristics are studied. The size of corona needle electrode is determined. Then, the corona discharge characteristics in N₂, CO₂, SF₆/N₂ and C₄F₇N/N₂ are studied. The breakdown voltage of the 6-gap gas switch and its stability with the gas type and pressure are studied. The experimental results show that the corona current is high in N₂. The corona current in air is lower and the corona discharge is stable in air. The addition of electric negative gas will greatly reduce the corona current. When air and N₂ are used as the switch gas, the breakdown voltage of the switch increases linearly with the increase of gas pressure, but there is a low breakdown voltage sometimes. When electric negative gas is mixed with N₂, the breakdown voltage is significantly higher. When the pressure of 1%SF₆/99%N₂ mixed gas is 0.18 MPa, the breakdown voltage is about 197.33 kV and the ratio of the standard deviation to the breakdown voltage is 1.50%.When 1% C₄F₇N/99%N₂ mixed gas is 0.15 MPa. The breakdown voltage is about 190.42 kV, and the standard deviation is 0.55%. This indicates that the mixed gas of C₄F₇N and N₂ has a significant effect on improving the breakdown voltage stability of multi-gap gas switch.