The breakdown characteristics of capillary discharge are measured in Ar and He gases within the pressure range from 120 Pa to 10 Pa, which is the range for lasing by capillary discharge. The experimental results indicate that at least ～10 kV of discharge voltage is required for the breakdown of gas filled in a capillary of 3 mm in diameter and 90 mm in length, which is much higher than that needed in parallel electrode system. The breakdown voltage is also greatly affected by the surface shape of electrode in low pressure. Studies show that the impedances of capillary for different lengths of gas column under the different discharge voltages represent the same character. The impedances reach the same minimum of ～5 Ω when the discharge currents reach the peak value, which makes it possible to obtain the same current peak value at the same discharge voltage for different lengths of capillary.