First-principles calculations in conjunction with the CALYPSO structure search method are performed to investigate the structural phase transitions of the perovskite stannates ASnO 3 (A = Ca, Sr, and Ba) under hydrostatic pressure up to 100 GPa. Two reconstructive phase transitions appear in CaSnO 3 , that is, from a perovskite state (Pv-Pnma) to a novel state that belongs to the post-perovskite family (pPv-Cmcm) and then undergoing another reconstructive transition to the so-called post-post-perovskite state (ppPv-Pnma) at higher pressure. In contrast, SrSnO 3 directly changes from Pv-Pnma phase to ppPv-Pnma phase under high pressure. However, BaSnO 3 only retains the ideal cubic perovskite structure up to 100 GPa without a phase transition. Subsequently, based on time-dependent density functional theory (TDDFT), quantum dots (QDs) fabricated by the pressure-induced stable structures of ASnO 3 interacting with ultrafast laser pulses are investigated. Strikingly, compared with traditional perovskite QDs fabricated by simple structure (Pm3̅ m), pPv-QDs based on the stable phase pPv-Cmcm of CaSnO 3 occur an obvious insulator−metal transition within a wide range of laser wavelengths and show enhanced optical absorption through size adjustment. In particular, CaSnO 3 pPv-QDs under high-intensity lasers exhibit nonvolatile memory characteristics, which demonstrates the potential applications for memory units and data storage devices.