The invention relates to a method for establishing a broadband model of a modularized multilevel current converter. The broadband model of the modularized multilevel current converter is formed by a bridge arm reactor and at least two valve towers through cascade connection, wherein each valve tower is formed by at least two sub-modules through cascade connection; the bridge arm reactor is formed by a series branch formed by an ideal reactor and an equivalent resistor and a stray capacitor through parallel connection; the capacitors of the sub-modules are formed by ideal capacitors as well as a lead-in inductor and a lead-in resistor thereof through series connection; and stray capacitors are connected between the incoming/outgoing lines of the valve towers. According to the method, the influences of the parasitic elements are fully considered in the broadband modeling process, so that the established broadband model of the modularized multilevel current converter is closer to the practical system and is higher in accuracy degree.