<p>The surface-emitting distributed feedback lasers generally operate in the asymmetric mode with low radiation loss and low radiation efficiency. Here, we propose a new broken-period distributed feedback terahertz quantum cascade laser (BP-DFB THz-QCL); an inverse design method based on the genetic algorithm, which is first introduced for the terahertz quantum cascade laser waveguide, is used to obtain the optimized structure of BP-DFB THz-QCL. The lowest loss mode of the broken-period structure is a high-radiation-efficiency mode that differs from the asymmetric mode of the second-order distributed feedback grating. Through simulations, it has been shown that this structure can achieve a surface photon loss rate of up to 137.5&#xa0;GHz, corresponding to an estimated radiation efficiency of 45.3%. The simulation results also demonstrate the high radiation efficiency characteristics of the device can cover a broadband frequency range by adjusting the grating slit width and grating period.</p>