Mixer is the core of wireless receiver, which is widely used in communication receiving system. In this paper, a single balanced diode mixer circuit with the characteristics of good linearity, low noise, low power consumption and good stability (RF frequency of 4.2 GHz, local oscillator frequency 4 GHz and intermediate frequency 200 MHz) is designed by using ADS software. Firstly, the 3 dB branch directional coupler and low-pass filter with central frequency in 4 GHz are designed with micro strip line, then the capacitance and inductance matching network circuit is designed. Finally, two mixer diodes are added to complete the design of the whole circuit. The ADS software is used to analyze and optimize the circuit. The simulation results show that the 1 dB compression point is 2.6 dBm, the noise figure is 6.89 dB, and the frequency conversion loss is greater than-10 dBm. The simulation results fully meet the design specifications, and the noise characteristics of the circuit are analyzed, which has important reference value for the design and optimize of single balanced diode mixer.