Abstract: In this paper,a new method of simulating diodes using three-dimensional field simulation software,Ansoft HFSS,has been proposed,which solved the problem that it is unavailable to simulate the orthogonality of two electric fields using the circuit sumulation software in some specific spatial hybrid integrated circuits.Now,this kind of circuit can be simulated using field simulation software directly with the method proposed,which improves the efficiency and accuracy.The diodes were replaced by the impedance boundary in HFSS,whose impedance was set equal to the impedance of the diode,then the matching circuit could be simulated.A finline single-balanced mixer was designed to validate this method.The measured return loss in the radio frequency port agree well with simulated result by this method from 40 to 60 GHz,which validates this method.