The study of new C–H silylation reagents and reactions remains an important topic. We reported that under Rh catalysis, silacyclobutanes (SCBs) for the first time were able to react with C­(sp2)–H and C­(sp3)–H bonds, however the underlying reasons for such a new reactivity were not understood. Through this combined computational and experimental study on C–H silylation with SCBs, we not only depict a reaction pathway that fully accounts for the reactivity and all the experimental findings but also streamline a more efficient catalyst that significantly improves the reaction rates and yields. Our key findings include: (1) the active catalytic species is a Rh–H as opposed to the previously proposed Rh–Cl; (2) the Rh–H is generated via a reductive elimination/β-hydride (β-H) elimination sequence, as opposed to previously proposed endocyclic β-H elimination; (3) the regio- and enantio-determining steps are identified; (4) and of the same importance, the discretely synthesized Rh–H is shown to be a more efficient catalyst. This work suggests that the Rh–H/diphosphine system should find further applications in C–H silylations involving SCBs.