A broadband microstrip patch antenna with multi-layer substrate for fuze application is designed. The multi-layer substrate is composed of the bottom layer of Si with low electric conductivity, the middle and the top layers of Si with high electric conductivity. An air cavity is fabricated by inductively coupled plasma (ICP) etching in the middle layer of Si to reduce the effective dielectric constant of the multi-layer substrate. The multi-layer substrate microstrip patch antenna is simulated and optimized by finite element method. The simulation results show that operating at 10GHz, the bandwidth and the gain of the multi-layer substrate microstrip patch antenna are 15.5% and 6.1dB respectively, which meet the needs of the application in fuze well.