In terms of the problem that synthetic aperture radar (SAR) in unmanned aerial vehicle (UAV) is easy to be attacked by high-power microwave (HPM) weapons in the complex electromagnetic environment of the battlefield, the field-circuit joint simulation of high-power microwave front-gate coupling of UAV’s SAR was carried out. The model of the SAR’s antenna is established in the CST software. The model of antenna is irradiated with a pulse-modulated sinusoidal signal to simulate the HPM signal, and the antenna port coupling voltage waveform is collected. On the basis of electromagnetic energy front-gate coupling, antenna port coupled voltage signal is injected into the RF front-end circuit modelof SAR, which fully simulated the coupling process of high-power microwave signal from field to circuit. The power input and output curves of RF front-end devices are simulated, and the curves for evaluating the high power microwave front-gate coupling effect of UAV’s SAR are given in combination with the damage or burnout threshold of the devices. The simulation results show that the low noise amplifier in the RF front-end circuit of SAR receiver is the main target of HPM signal damage. At the same time, HPM signal will trigger a spike leak in the PIN limiter, which threatens the low noise amplifier of the subsequent circuit.