A new persistent yellow-emitting phosphor CaGa2S4: Eu2+, Ho3+ was prepared by a solid-state method. The luminescence properties, including thermoluminescence (TL) glow curve and its spectral decomposition, as well as the long decay time curve, were studied. The results revealed that a new trapping level with a suitable depth was created due to co-doped Ho3+, which led to the long afterglow at room temperature. Trapping depths were evaluated by a TL glow curve fitted by a general order kinetics formula. A mechanism for the long-duration phosphorescence from Eu2+ in CaGa2S4: Eu 2+, Ho3+ was also proposed.