Terahertz quantum cascade lasers (THz QCL) with dual optical combs have important applications in spectral detection, ranging, and imaging. The dual-comb signal is heavily dependent on the THz coupling optical power. The THz QCL excitation light is linearly polarized, and a linear polarizer is inserted into the optical path of the dual optical comb, and the polarizer is rotated to adjust the THz light intensity. The dependence of the THz QCL dual-comb spectrum and power on the polarization angle is systematically studied to lay the foundation for the realization of a highly stable THz dual-comb light source and application.