A terahertz fourth harmonic mixer based on anti-parallel Schottky diode pair is introduced, and its Radio Frequency (RF) operating range covers 400 GHz to 600 GHz. The mixer use a multi-point ground structure at the RF ends, which effectively reduces the return loss of RF port compared to the traditional single point ground structure. By adopting an integrated RF-end design method, the number of matching branches is reduced by 30% during the design process compared to traditional methods, thereby enhancing design efficiency. The measured results show that the typical value of conversion loss is 20 dB and the optimal value is 14 dB in the whole working band when the Local Oscillator (LO) power is in the range of 7～13 dBm.