In view of the broad application prospects of the electro-demulsification method in oil field production，in order to improve the mechanism of micro-droplet coalescence of electro-demulsification，from the dynamics progress of disperse phase droplets deformation，proximity，rupture and coalescence，the research progress of coalescence mechanisms at home and abroad was systematically reviewed. Firstly，The effects of physical factors were first described in terms of moisture content，viscosity， conductivity，and surface tension of the droplets；secondly，the effect of electric field parameters，including electric field form， intensity，and frequency，on the coalescence velocity was reviewed significantly.