In order to improve the red luminous properties of luminescent fibers, Sr2MgSi2O7:Eu2+, Dy3+ and light conversion agents were treated with silane (KH560), aluminate (DL-411-A), and aluminum zirconium coupling agents (LD-139-3) to prepare composite luminescent materials. And then they were added to a polyacrylonitrile (PAN) fiber-forming polymer and through wet spun to form composite red light-emitting fibers. The surface morphology, phase structure, and luminescence properties of the composite red light-emitting fibers were characterized by scanning electron microscopy, X-ray diffraction, fluorescence spectrometry, and afterglow brightness tester. Results showed that all of the three kinds of coupling agents influenced the red light of the luminescent fibers. The aluminate ester coupling agent had more effect than that of the other two coupling agents. After treatment with the aluminate coupling agent, the surface of the luminescent material became rough and adhered to the particles of light conversion agent. The intensity of the emission peak of the luminescent fibers at 470 nm decreased, and the emission peak intensity at 595 nm improved. The initial afterglow brightness and afterglow duration remained unchanged after 15 min of ultraviolet light excitation, as well as the color purity increased by approximately 1.6 times.