Dual-comb realized by terahertz quantum cascade lasers (THz QCL) has important applications in spectral detection, distance measurement and imaging. The dual-comb signal is heavily dependent on the THz coupling optical power. The THz QCL light is linearly polarized, and a linear polarizer is inserted into the optical path of the dual-comb. The polarizer is rotated to achieve the effect of adjusting the THz light intensity. The dependence of the THz QCL dual-comb spectrum and power on the polarization angle is systematically investigated and it lays the foundation for the realization of a highly stable THz dual-comb light source and application.