Microdischarge behaviours in a gap between the plane electrode and a charged conducting spherical particle moving in the presence of external electric field have been investigated. The microgap studied has distinctive features: (a) the field strength in the microgap changes very rapidly with the motion of the sphere even if the applied external electric field is static, (b) the boundary of the microgap changes with time and (c) the potential difference across the microgap is influenced from the occurrence of discharge due to the neutralisation of charge on the sphere by the charge carrier in the discharge itself. The random appearance of an initiating electron required for the development of an avalanche and the rapid changes of electric field, gap boundary and potential difference result in the statistical behaviours of microdischarge. The statistical characteristics at the microdischarge threshold and on the microdischarge length have been measured, and the microdischarge mechanism has been discussed to explain the characteristics.