Recently, Terahertz Time Domain Spectroscopy(THz-TDS) has been proposed to measure electron density of plasma. Nevertheless, the method still needs to be further verified by estimating the reliability and practicability using theoretic or other experimental methods. In this work, the THz-TDS technique is applied to measure the electron density of Inductively Coupled Plasma(ICP). The ICP discharge is operated in the H-mode with a RF power supply of 13.56 MHz at various input powers from 250 W to 400 W under argon pressures from 39 Pa to 99 Pa. It is observed that electron densities monotonically increase with the increase of RF input power and argon pressures, and the measured electron densities are in the range of 10¹³~10¹⁴ cm^-3 under the given conditions. Meanwhile, a fluid numerical simulation based on COMSOL Multiphysics using drift-diffusion model is adopted to investigate the characteristics of the discharge plasma at the given powers and pressures. The results show that the simulated electron densities are in qualitative agreement with the measured results, which supports that the measurement method using THz-TDS is feasible. Furthermore, the variation trends of the electron density with the pressures obtained by simulation and measurement are also similar, which further verifies the application potential of the THz-TDS for non-invasive plasma electron density measurement.