In this paper, a package design for die-stacking system was presented. The cavity-substrate was fabricated by lamination and mechanically milling technology. Hybrid interconnection including both wire bonding (WB) and flip chip (FC) was used. The stacked dies were embedded into the cavity substrate. Finally, four chips and twenty-two passives were packed in a 16mm*16mm standard ball grid array (BGA) package. In contrast with earlier 2D package design version, the packaging area was reduced by 40% and the package height was decreased by about 500μm. In addition, the fan-out area for the stacked die was tripled. The design progress and how the design was realized were delicately elaborated.