${\mathrm{Ca}}_2\mathrm{N}$, a prototypical electride with intrinsic interstitial anionic electrons (IAEs), exhibits pressure-induced electronic phase transitions. Previous studies have revealed a pressure-induced metal-semiconductor transition in ${\mathrm{Ca}}_2\mathrm{N}$ at relatively low pressures; however, the evolution of its crystal structure and the role of interstitial electrons under extended compression remain unclear. Here, we combine first-principles calculations with crystal structure prediction to investigate the structural and electronic evolution of ${\mathrm{Ca}}_2\mathrm{N}$ up to 120 GPa. We identify six stable high-pressure phases, including $Fd\text{−}3m$, $I\text{−}42d$, $P2$, $Fm\text{−}3m$, $R\text{−}3m\text{−}\mathrm{II}$ and $I4/mmm$ for ${\mathrm{Ca}}_2\mathrm{N}$. Analysis of the pressure-dependent evolution of IAEs reveals a nonmonotonic electronic transition from metal to semiconductor and back to metal. Upon compression, extended interstitial electron states gradually transform into localized zero-dimensional states, resulting in electron confinement and gap opening. At higher pressures, the reduced interstitial volume promotes hybridization between interstitial electrons and Ca-$d$ states, leading to reentrant metallization. These results establish the high-pressure structural and electronic phase diagram of ${\mathrm{Ca}}_2\mathrm{N}$ and provide a microscopic mechanism linking interstitial electron behavior to electronic transitions in electrides, advancing understanding of pressure-driven phenomena in these materials.

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• Density of states
• Electronic structure
• Local density of states
• Phase transitions
• Structural properties
• Electrides