The invention discloses a multi-objective optimization based parameter matching method for a power system of a battery electric vehicle. The method includes: establishing a parameter matching optimization module by taking multiple vehicle performance indexes including a maximum speed, an acceleration time, 100km power consumption and the like as optimization objectives and taking a transmission ratio as an optimization variable; taking most fundamental performance indexes of a type of the vehicle as constraint conditions to obtain a feasible region of the transmission ratio, and adopting a multi-objective genetic algorithm for solving optimization problems in the feasible region; working out Pareto optimal solution sets under the conditions of fixed-transmission-ratio transmissions and two-gear transmissions, and taking the Pareto optimal solution sets as alternative sets; comprehensively comparing the alternative sets of the different motors to determine a final parameter matching scheme for sample vehicle development.