All-solid-state Li-ion battery based on solid electrolyte materials is a promising next-generation Li-ion battery technology with intrinsic safety, high energy density, and enhanced cyclability. The key problem in enabling this new battery technology is the high interfacial resistance and interfacial degradation at the solid electrolyte-electrode interfaces. In this presentation, I will show how we use computational modeling to provide unique insights into the fundamental mechanisms at these buried interfaces, which are difficult to access in experiments. I will first demonstrate using first principles computation to predict various materials properties of the solid electrolyte materials with little experimental input. In addition, we systematically investigate and compare the electrochemical stability and chemical stability of the solid electrolyte-electrode interfaces, and study how these interfaces affect the interfacial resistance, low cyclability, and mechanical failure in all-solid-state Li-ion batteries. Our computation results suggest the formation of decomposition interphase layers in all-solid-state Li-ion batteries and the significant effects of the interphase layers on the electrochemical performance of the all-solid-state Li-ion batteries. Different interfaces between solid electrolyte and electrode materials may have different problems at the interfaces, which require different interfacial engineering strategies to resolve. The mechanisms of artificial layers to improve the interfacial properties are revealed by our computation. This computational study provides novel insights and general guidance for interfacial engineering in all-solid-state Li-ion batteries.