The light output performance of scintillation crystals can be affected by the temperature of the crystal. Gd₃(Ga, Al)₅O₁₂∶Ce(GAGG∶Ce) scintillation crystals are widely used in medical imaging, radiation monitoring, high-energy physics, and other fields. To study the temperature dependence of the light output of GAGG∶Ce crystals, this paper designed an experiment with crystal temperature as a single variable. The full energy peak position of seven energy levels of γ-rays ranging from 121.8 keV to 1 112.1 keV was measured within the temperature range of -30 ℃ to 60 ℃. The curve of the light output of GAGG∶Ce crystals changing with temperature was obtained, and the linear relationship between the light output of the crystal and temperature was analyzed. A linear function was used to fit the energy linearity of the corresponding channel positions for seven energies ranging from 121.8 keV to 1 112.1 keV at different temperatures. The determination coefficient R² of the linear fit was greater than 0.999 9, demonstrating that GAGG∶Ce crystals have good energy linearity.