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We present a method for calibrating a commercial thermal camera adopted to accurately measure the temperature change of the sample in a laser-induced temperature modulation spectrum (LITMoS) test, which is adopted for measuring two crucial parameters of the external quantum efficiency <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mi>η</mi><mrow><mi>e</mi><mi>x</mi><mi>t</mi></mrow></msub></mrow></semantics></math></inline-formula> and the background absorption coefficient <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mi>α</mi><mi>b</mi></msub></mrow></semantics></math></inline-formula> for assessing the laser cooling grade of the rare-earth-doped materials. After calibration, the temperature resolution of the calibrated thermal camera is better than 0.1 K. For the cooling grade Czochralski-grown 5% Yb³⁺:LuLiF₄ crystal, the corresponding values of <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mi>η</mi><mrow><mi>e</mi><mi>x</mi><mi>t</mi></mrow></msub></mrow></semantics></math></inline-formula> and <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mi>α</mi><mi>b</mi></msub></mrow></semantics></math></inline-formula> are LITMoS = measured to be <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mi>η</mi><mrow><mi>e</mi><mi>x</mi><mi>t</mi></mrow></msub><mo>=</mo><mn>99.4</mn><mo> </mo><mrow><mo>(</mo><mrow><mo>±</mo><mn>0.1</mn></mrow><mo>)</mo></mrow><mo>%</mo></mrow></semantics></math></inline-formula> and <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mi>α</mi><mi>b</mi></msub><mo>=</mo><mn>1.5</mn><mo> </mo><mrow><mo>(</mo><mrow><mo>±</mo><mn>0.1</mn></mrow><mo>)</mo></mrow><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>4</mn></mrow></msup><mo> </mo><msup><mrow><mi>cm</mi></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup></mrow></semantics></math></inline-formula>, respectively.