IceTop is the surface component of the IceCube Neutrino Observatory at the geographical South Pole. It is designed to measure the air showers of cosmic ray with energies from PeV up to EeV. In general it is reasonable to assume that the muon signal becomes significant for a large distance from the shower axis, since they are overwhelmed by the signal from electromagnetic components at close to the shower axis. Considering the charge signal distribution, a parameter sensitive to the muon content was defined and estimated, which is the sum of the charge signals divided by the total number of tanks and the area of the tanks at a fixed distance from the shower axis. In this talk the estimated muon parameter based on the charge distribution will be presented. Its dependence of the high-energy hadronic interaction models will be discussed as well.