Smart fluorescent materials have attracted much attention due to their promising applications in various fields. Here, we demonstrate a reversible fluorescence switching of CsPbI3 nanocrystals (NCs) using photochromic AgI NCs as the photosensitizer. Upon light irradiation, AgI NCs are decomposed into metallic Ag and elemental I2, leading to the formation of Ag-CsPbI3 heterostructures. Because Ag has a lower Fermi level than that of CsPbI3, excited electrons will transfer from CsPbI3 to Ag, resulting in the quenching of photoluminescence emission. When the composite is stored in the dark, metallic Ag is oxidized into AgI, and the PL emission of CsPbI3 NCs can be recovered. The application of the AgI/CsPbI3 system has been demonstrated as a rewritable platform. This work may shed light on the exploration of CsPbX3 NCs for applications in smart fluorescent materials.