In this work, an efficient polymer‐based organic afterglow system, which shows reversible photochromism, switchable ultralong organic phosphorescence (UOP), and prominent water and chemical resistance simultaneously, has been developed for the first time. By doping phenoxazine (PXZ) and 10‐ethyl‐10H‐phenoxazine (PXZEt) into epoxy polymers, the resulting PXZ@EP‐0.25 % and PXZEt@EP‐0.25 % films show unique photoactivated UOP properties, with phosphorescence quantum yields and lifetimes up to 10.8 % and 845 ms, respectively. It is found that the steady‐state luminescence and UOP of PXZ@EP‐0.25 % are switchable by light irradiation and thermal annealing. Moreover, the doped films can still produce conspicuous UOP after soaking in water, strong acid and base, and organic solvents for more than two weeks, exhibiting outstanding water and chemical resistance. Inspired by these exciting results, the PXZ@EP‐0.25 % has been successfully exploited as an erasable transparent film for light printing. A series of efficient phosphorescence materials were developed by embedding phenothiazine, phenoxazine, and 10‐ethyl‐10H‐phenoxazine into epoxy polymers. It is found that the polymer film involving phenoxazine shows reversible photochromism, switchable ultralong organic phosphorescence, and prominent water and chemical resistance simultaneously. In addition, its potential application in erasable light printing has also been demonstrated.