Abstract: The surface of a launch vehicle and its engine will be charged during the flight, with drastic consequences when the electronic static charges have accumulated to some extent. Among many causes, this paper focuses on the electrification process of the engine's jet flow and friction. The calculation model of these two kinds of electrification is established. The equivalent charging current of these two kinds of electrification is determined combined with the electrostatic measurement experiment, thus the maximal charging potential is analyzed, to provide a guidance for the product design and the system protection.