Abstract: In order to improve the functional density of microwave front-end, a miniaturized system-in-package (SiP) module based on a multi-cavity stacking integration structure is designed using high-temperature co-fired ceramic (HTCC) technology, which realizes the high-density integration of transmit/receive frequency conversion, local oscillator generation, transmit amplification and modulation, IF amplification and other functions. The vertical stacking of HTCC substrates is realized by implanting ball grid array (BGA) in each cavity, which effectively improves the integration density, and the overall size is only 45 mm×45 mm×10 mm. By investigating the vertical interconnection structure of multistage transition and electromagnetic coupling characteristics in the module, the low-loss interconnection transmission of RF signals and high electromagnetic isolation between internal sensitive units are achieved. At the same time, the finite element simulation results of thermal and mechanical stress indicate that the integrated approach offers good heat dissipation and robust resistance to mechanical vibration. A prototype of the SiP is fabricated and tested. The measurement results show a transmit power greater than 47.7 dBm, a receive noise figure below 3.5 dB, and a receive link gain exceeding 85 dB. This technology provides an effective technical solution for the integration of microwave front-end with high density and high reliability.