To enhance the protective effectiveness of the Beidou Navigation Satellite System (BDS) and the Global Positioning System (GPS) against high-power microwave, we adopted the method of field-circuit collaborative simulation design to analyze the response characteristics of the BDS/GPS antenna under high-power microwave irradiation. The coupling voltage was obtained by simulation. To achieve protection against high-power microwave, a two-stage protection circuit was designed. By constructing steady-state and transient circuit models, the insertion loss and leakage voltage were analyzed according to simulation, and the circuit was processed. The test results show that the leakage power of the protective circuit was less than 0.5 W under HPM-NS injection of 2 kW, the leakage voltage was less than 12 V under HPM-UWS injection of 1 411 V, and this proposed circuit structure can achieve effective suppression of high-power microwave. The protection circuit was assembled into the BDS/GPS antenna, and the test results show that the navigation systems can operate normally.