Abstract: Due to requirements of the wideband, high transfer rate, high power consumption and high integration, design of a system in package (SiP) module based on AlN multilayer high temperature co-fired ceramic (HTCC) substrate is studied in this paper. The AlN multilayer HTCC substrate is designed, the SiP module design and simulation are carried out, thermal simulation and analysis of the module assembly structure are conducted and packaging process is optimized. A small, lightweight and highly integrated SiP module is developed finally, which shows good reliability by environmental test. This research result can provide a reference for design of the small, lightweight and highly integrated SiP module.