Abstract: To study the high-power microwave front door effect of system-level RF equipment, the injection method was used to conduct experimental research on the RF front end composed of filter, circulator, low-noise amplifier and power amplifier of a 4G base station. The results show that the rising and falling edges of the high-power microwave pulse are strongly reflected by the RF front-end filter, and the reflection of the pulse flat top section is small. The reflected waveform spikes on the rising and falling edges, and the flattened part in the middle of the pulse, showing that the rich out-of-band frequency components of the filter contained in the steep rising and falling edges of the high-power microwaves are reflected, resulting in weakened pulses passing through the filter. After passing through the filter, the high-power microwave pulse can enter the upstream channel low noise amplifier from the circulator, and then be reflected, circulate into the downlink channel power amplifier, be reflected again, and then loop through the injection port output. High-power microwave pulses traveling through two reflection loops were detected in the experiment. This shows that under high-power pulse conditions, the downlink channel power amplifier originally isolated by the circulator is also at risk of damage from the high-power microwave pulse entering the upstream channel. This study has certain reference significance for the study of system-level high-power microwave front door effect.