In this work, we generalized our recently developed analytic Fermi's golden rule (FGR) rate theory of VSC by incorporating many molecules and many cavity modes for both 1D and 2D cases. In particular, we evaluated the photon mode density of states (DOS) inside a 1D FP cavity and found that it gives rise to a van-Hove-type singularity at 𝑘 ‖ = 0; for a 2D FP cavity, it is found that due to the cavity modes with 𝑘 ‖ > 0 propagating outside the cavity and caus-ing additional cavity loss, the modified photon mode DOS still remains dominant around the bottom of the dispersion band where 𝑘 ‖ = 0, which are the keys to account for the normal incidence condition of the VSCmodified chemical reaction rate constant. The current theory successfully explains the resonance condition for the observed VSC effect and provides a microscopic understanding of why only at the normal incident angle there is a resonance effect.