Composite red luminescent material Sr₂MgSi₂O₇: Eu²⁺, Dy³⁺/light conversion agent is a kind of long-afterglow luminescent material prepared with a light conversion agent and Sr₂MgSi₂O₇: Eu²⁺, Dy³⁺ at a certain mass ratio. This material has excellent characteristics (i.e. high brightness and good stability) of Sr₂MgSi₂O₇: Eu²⁺, Dy³⁺. Also, it can emit a red light. In this paper, silane coupling agent (i.e. KH560), aluminate-coupling agent (i.e. DL-411-A), zircoaluminate coupling agent (i.e. LD-139-3) and their composite coupling agents (i.e. A: composite of silane coupling agent and aluminate coupling agent; B: composite of silane coupling agent, aluminate coupling agent and aluminum zirconium coupling agent) were used to prepare the composite red luminescent materials. The effects of coupling agent on the luminescence properties were investigated. The surface morphology, phase structure and luminescence properties of the composite luminescent materials were characterized by scanning electron microscope, X-ray diffractometer, fluorescence spectrometer and afterglow luminance meter. The results show that three coupling agent all can improve the luminescence performance of composite luminescent materials, and the composite coupling agent has a better effect. The surface of Sr₂MgSi₂O₇: Eu²⁺, Dy³⁺ becomes coarse and adheres to the massive light conversion agent particles when a composite coupling agent B is used. In this case, the emission peak intensity of the sample is increased by 1.89 times at 605 nm, but decreased by 72% at 470 nm, the initial afterglow brightness is increased by 1.86 times, and the color purity is enhanced by 1.87 times.