The inflatable composite cross-arm served under long-term outdoor conditions may deteriorate its sealing characteristic and cause leakage. When the internal gas escapes and the external humid air invades the cross-arm, it will cause flashover inside the cross arm, threatening the security and stability operation of power systems.Therefore, this article explores the influence of leakage on the inner insulation characteristic of the inflatable composite cross-arm. The influences of different internal temperature and humidity conditions caused by the cross-arm pressure leakage on the flashover voltage and leakage current are studied through experiments, and the flashover voltage, leakage current, and pulse number are analyzed. The results show that the influence of temperature on the internal insulation of the crossarm is related to the humidity, and the difference of temperature causes the difference of internal condensation state and then affects its internal insulation performance. Under the same temperature conditions, humidity significantly affects its internal insulation.The absolute humidity values at 20 ℃, 50 ℃ and -30 ℃ increase from 3.5 g/m³ to 17.3 g/m³, and the flashover voltage amplitudes decrease by 24%, 24.7% and 38.7% respectively. Through the leakage current amplitude and pulse statistics combining with microscope observation, It is shown that the inner surface of the cross-arm had different condensation states at different temperatures. The increase in temperature makes the condensation disappear and the flashover voltage increase. The increase in absolute humidity causes aggravation of condensation, which reduces the flashover voltage and increases the leakage current amplitude.