Polarization-induced charge density in modulation-doped AlxGa1-xN/GaN heterostructures is extracted through the simulation of the Schottky Capacitance-Voltage (C-V) characteristics. C-V measurements were made on Pt Schottky contacts on modulation-doped Al0.22Ga0.78N/GaN heterostructures. The C-V characteristics were simulated numerically using the three-dimensional Fermi model.Influence of sample parameters on C-V characteristics is analized by the simulation.Polarization-induced charge density,n-AlGaN doping level and Schottky barrier height have different influences on the C-V characteristics,and thus the polarization-induced charge density can be extracted accurately.The polarization-induced sheet charge density at the heterointerface is extracted to be 6.78×1012cm-2 in the Al0.22Ga0.78N/GaN heterostructure with the Al0.22Ga0.78 N thickness of 45nm.This work provides a method for quantitative analysis of the polarization-indeced charge in modulation-doped AlxGa1-xN/GaN heterostructures.