Stacking pressure plays a critical role in maintaining the electrochemical performance of solid-state batteries (SSBs), including anode-free solid-state batteries (AFSSBs). Nevertheless, the influence of stacking pressure on interface properties remains insufficiently understood. In this work, we found that stacking pressure could improve both anode and cathode interface electrochemical properties, but the enhancement of the cathode side is considerably smaller than that observed at the anode interface, indicating that pressure primarily benefits the anode side. We also establish a correlation among stacking pressure, anode and cathode potentials, interface resistances, Li deposition morphology, and stress distribution in AFSSBs. Our results show that increasing the stacking pressure leads to higher reversible capacity, lower Li plating/stripping overpotentials, more uniform Li deposition, and a more homogeneous stress distribution. Achieving uniform Li deposition is key to reducing the required magnitude of stacking pressure. This study deepens the understanding of interfacial dynamics in AFSSBs and paves the way toward developing high-performance SSBs operable under low stacking pressure.