The calculation methods have been developed for estimating the power and power imbalance, for that there is no disscussion on calculation method of power balance in detail currently. According to the results of theoretical simulation, the center position of temporal profile full width half maximum is fixed as the base point of power balance calculation for the flat-top pulse. Photo-electricity conversion component, oscillograph, and energy calorimeter are used to measure beam synchronization of arrive target, temporal profile and energy. Detailed results of the power and the power imbalance of laser facility from these calculations are proposed, and the uncertainty is analyzed. Consequently, the measurement technique and methods of multi-beam laser power balance are given.