A terahertz fundamental up-conversion mixer with a high Local Oscillator（LO）/Radio Frequency （RF） and local oscillator /Intermediate Frequency（IF） port isolation was presented based on IHP 0.13μm SiGe BiCMOS process. The mixer adopted Gilbert’s double-balanced structure, and the local oscillator signal was transmitted through the Coplanar Waveguide（CPW） to suppress the transmission asymmetry caused by the strong parasitic coupling effect in the transmission process, reducing the characteristic of LO/RF port isolation deterioration caused by the asymmetry. By adopting an asymmetric switch interconnection structure, the imbalance of the parasitic coupling of the local oscillator signal at the collectors of the switching transistors was reduced, and the cancellation efficiency of the local oscillator signal at the collectors of the switching transistors was improved. The leakage of the local oscillator signal was suppressed at the port of intermediate frequency by arranging the position of the transconductance transistors in a reasonable layout. The post-simulation results show that，under the power supply voltage of 2.2 V，the local oscillator signal is 230 GHz，and the intermediate frequency signal is 2-12 GHz. When the up-conversion mixer works at 218-228 GHz, the LO/RF port isolation is greater than 24 dB, LO/IF port isolation is greater than 20 dB，and the conversion gain is -4 dB to-3.5 dB. The output 1 dB compression point is -14.8 dBm when the intermediate frequency signal is 10 GHz. The DC power consumption is 42.4 mW, and the core area of the chip is 0.079 mm2. The up-conversion mixer can be applied to a wireless transmission system using a high-order quadrature amplitude modulation method.