Abstract: In order to study the characteristics of sub-micron air gap discharge, a nano-positioning system is used to carry out gas discharge experiments with electrode spacing of 0.3-10 μm under atmospheric pressure. The breakdown voltages of stainless steel, brass, copper and aluminum electrodes are measured, and it is found that the measurement results are obviously deviated from the Paschen curve. When the electrode spacing is reduced below 5 μm, the effect of the material work function on the air gap breakdown voltage is more significant, but it is not obvious in the range of 5-10 μm spacing. Through the study of breakdown field strength and field emission current density, it is found that when the electrode spacing is less than 5 μm, field-induced electron emission gradually becomes the dominant discharge mechanism, resulting in the breakdown voltage deviating from the Paschen curve and the influence of work function becoming larger. By comparing the numerical calculation results of the breakdown voltage, it is shown that only the field-induced electron emission needs to be considered when the spacing is in the range of 0.3-2 μm. Studying the discharge characteristics of micro-gaps can provide a basis for the insulation design of micro-devices.