Hill fire hazards on transmission and distribution lines due to various factors affect the safe operation of the lines. The current study does not consider the effect of ground capacitance current on fire impedance characteristics under the line. This paper takes 35 kV line under the mountain fire flame impedance characteristics as the test object, build different to ground capacitance of the mountain fire test platform, put forward the mountain fire ground fault theoretical model, through simulated line under the mountain fire test on the flame completely bridged gap order eucalyptus, shrubs and straw flame impedance characteristics of curve fitting, verify the vegetation mountain fire triggered by the line single-phase grounding is a high resistance ground, research and analysis of the vegetation flame impedance characteristics of the impact mechanism. Experimental research shows that the occurrence of mountain fire fault line fault degree and ground capacitance current is positively correlated; flame temperature is one of the main factors affecting flame impedance, flame impedance and flame temperature does not strictly show a negative correlation; different vegetation types triggered by mountain fire flame impedance characteristics vary greatly, arc discharge will seriously weaken the vegetation flame insulation characteristics, flame completely bridged gap stage before and mid-term flame impedance of the main influencing factors are flame temperature and flame height, flame completely bridged gap stage late flame impedance of the main influencing factors into the ash content of vegetation. The study of vegetation flame impedance characteristics can provide technical reference for transmission and distribution lines to prevent line failures caused by hill fires.