THz waves are very good candidates for high-capacity wireless links since they offer a much higher bandwidth than RF frequencies. Photonic crystal (PC) offers a new opportunity for integrated THz wave devices. It permits the integrated devices to be miniaturized to a scale comparable to the wavelength of the electromagnetic wave. Considering their governing properties such as photonic band gap (PBG) and photon localization effect to control electromagnetic wave propagations, PC-based THz modulator has attracted much attention. Tunability strategies include mechanical control, electrical control, magneto static control, temperature control and optical pumping. However, the development of high-speed THz wireless communication system is limited by the low modulation depth and rate of previously reported modulators. In this paper, we propose a novel magnetic-controlled THz modulator based on a magnetized plasma PC consisting of line defects and a point defect. InSb, a semiconductor with high electron mobility, is introduced into the point defect. According to the magneto-optical effect, the refractive index of InSb changes rapidly under the control of the applied magnetic field (MF) intensity. Then the mode frequency in the point defect changes dynamically. The structure is based on a two-dimensional PC constructed by triangular lattice of Si rods in air. Based on the magneto-optic effect, the magnetized plasma defect mode in the THz regime can be decomposed into the left- and right-handed circularly polarized light when the applied magnetic field is parallel to the direction of the THz wave. And the difference in effective refractive index between the left- and right-handed circularly polarized light increases with the applied uniform magnetic field increasing. Therefore the on/off modulation of left- and right-hand circularly polarized light can be realized. The steady-state field intensity distribution and the time domain steady state response of TE wave propagating parallelly to the external magnetic field are simulated by the finite-difference-time-domain and finite element method. The simulation results show that PC-based mode transfer modulator has the potential application to THz wireless broadband communication system with a good performance of high contrast ratio (25.4 dB), low insertion loss (0.3 dB) and high modulation rate (～4 GHz). It is convenient to load the modulation signals in an easy MF application way. The device designed is leading the way to extend the application of THz wireless communication filed with advantages of small size, low insertion loss, and high extinction ratio.