The large interfacial resistance seriously restricts the development of all-solid-state lithium batteries (ASSLBs). In our work, first-principles calculations are employed to investigate the interfacial properties on lithium (Li) metal anode/Li6PS5Cl solid electrolyte (LPSCl) interface system as well as buffer layers (Li2S) effects. The stable interface structures, Li/LPSCl, L2S/LPSCl and Li/L2S, are established at atomic level. We find that PS4 tetrahedral structure has been seriously destroyed in Li/LPSCl interface, whereas the presence of Li2S buffer layers may smooth the interface without PS4 tetrahedral damage occurred. In addition, the electronic structure of interface indicates that solid electrolyte interphases are not easy to form on LPSCl surfaces considering buffer layers effects, which may improve the stability of anode/solid electrode interface. Moreover, the calculated energies of exchange ions between Li metal and solid electrolyte with buffer layers suggest that the Li2S interposition can suppress the atoms diffusion in LPSCl layers, and provide a smooth interface structure, which may promote the stability of Li/LPSCl interface. This work on the atomic scale will offer a useful perspective for designing high performance of solid electrolytes to enhance good cyclability in ASSLBs.