Abstract: To study the breakdown characteristics of gases at micro-gaps, discharge experiments are carried out at variable air pressures from 1-100 kPa with a gap distance of 3-100 μm. It is found that the breakdown voltage curve deviates from the Paschen curve for spacing below 10 μm, and the breakdown voltage changes with air pressure when the fixed spacing only changes the pressure, which is different from the long gap, and the breakdown voltage decreases with increasing air pressure for 3-5 μm. By solving the equation for the ion number density near the cathode, it is found that there is a high ion number density near the cathode under the micro-gap condition, which increases with the increase of air pressure and decreases with the increase of electrode spacing. The higher the ion density, the stronger the ion additional electric field will be formed near the cathode surface, which will promote field emission after coupling with the applied electric field, and breakdown will occur more easily. The ion-enhanced field-effect coefficient γ' is calculated and compared with the Townsend secondary emission coefficient γ. It is found that the ion-enhanced field effect has the strongest influence on the gap discharge below 5 μm, and its influence gradually weakens with the increase of the spacing. The breakdown process after 10 μm can be explained by the Townsend theory.