Own to its fine granularity and sub-millimeter position information, scintillating single crystal fibers (SSCFs) hold great potential for various applications such as electromagnetic calorimeters, positron emission tomography, and radiotherapy dosimetry. The light response uniformity of scintillating fibers is an important parameter for precise measurements of ionizing radiation. Three methods were designed to investigate the light response uniformity of the 184-mm-long LuAG:Ce SCCF. Relatively longitudinal-distributed uniformity of cerium element was obtained in this SSCF. The scintillation light attenuation coefficient of the SSCF is 0.27 cm−1 induced by X-ray photons with single-end readout mode and about 0.29 cm−1 induced by gamma rays with dual-end readout mode. The Ce3+ ions self-absorption along the longitudinal light propagation process is one of main reasons for the scintillation light attenuation. Weakening the Ce3+ ions’ self-absorption effect is a possible way to improve the light response uniformity of the LuAG:Ce SSCF.