BaSi2O2N2:Eu2+ phosphor was successfully synthesized by using a simple solid-state reaction method. Its properties were systematically investigated utilizing XRD, photoluminescence, excited state decay curve, afterglow emission spectra, and thermoluminescence (TL) glow curve. With increasing temperature, its emission intensity decreases with the broadening full widths at half maximum. Particularly, its temperature-dependent afterglow emission spectra were investigated for the first time. Based on the information from TL glow curve, temperature-dependent afterglow decay curves, and afterglow emission spectra, a model was constructed to explain the mechanism of afterglow. This study provides a new perspective to use the temperature-dependent luminescence properties for studying the afterglow processes of long-lasting phosphorescence phosphors.