In order to compare and analyze the characteristics of two kinds of structure mixer through simulation design and measurement, the 250 GHz sub-harmonic mixers of suspended microstrip-line and conventional microstrip-line were designed respectively based on the Hammer-Head filter structure, combined with three-dimensional Schottky diode model and three-dimensional electromagnetic model. The results show that in the radio frequency(RF) range of 230-270 GHz, the conversion loss of single sideband converter was 8.6-12.7 dB for suspended microstrip-line mixer, while that was 8.4-11.4 dB for ordinary microstrip-line mixer with RF range of 220-260 GHz. Contrast results showed that the bandwidth of the suspended microstrip-line mixer was larger than that of the conventional microstrip-line mixer, but its flatness was worse. Finally, considering some undesirable factors introduced in the micro assembly processes, the simulation was calculated and compared with the measuring data, it was found that the results matched well.