Photon-coupling and electron dynamics are the key processes leading to the photocatalytic activity of plasmonic metal-semiconductor nanohybrids. To better utilize and explore these effects, a facile large-scale synthesis route to form Ag@AgCl cubic cages with well-defined hollow interiors is carried out using a water-soluble sacrificial salt-crystal-template process. Theoretical calculations and experimental probes of the electron transfer process are used in an effort to gain insight into the underlying plasmonic properties of the Ag@AgCl materials. Efficient utilization of solar energy to create electron-hole pairs is attributed to the significant light confinement and enhancement around the Ag/AgCl interfacial plasmon hot spots and multilight-reflection inside the cage structure. More importantly, an ultrafast electron transfer process (150 fs) from Ag nanoparticles to the AgCl surface is detected, which facilitates the charge separation efficiency in this system, contributing to high photocatalytic activity and stability of Ag@AgCl photocatalyst towards organic dye degradation.