As a typical load of an aircraft power system, the aviation static inverter (ASI) brings about undesirable low-frequency ripple current on the aeronautic dc bus, which seriously deteriorates the power quality of aeronautic grid. Based on the double-Fourier switching function method, the input current of the inverter unit is analyzed. The corresponding expressions of the dc component, the second harmonic current, the mth harmonic current with regard to the carrier frequency, and the sideband harmonic current are given. In addition the equivalent circuit model of the second harmonic current that spreads to the high-voltage dc bus is derived. This model reveals the generation and propagation characteristics of the low-frequency input ripple current of ASI and its impact factors. Simulation and experimental results are shown to validate the theoretical analysis.