The effects of pyrolysis temperature on the composition and distribution of three-phase products from distillers’ grains (DGs) were investigated. Gas chromatography, gas chromatography-mass spectrometry, and Fourier-transform infrared spectroscopy were used to analyze the composition and structure of the gas, liquid, and solid products. The formation of gases and bio-oil during DG pyrolysis was closely related to components such as crude protein, cellulose, lignin, and crude fat. At low temperatures (≤ 500 ℃), the main reactions involved hemicellulose, crude protein, cellulose, and crude fat. At high temperatures (600~800 ℃), the main reaction was lignin decomposition, which formed gases and bio-oil. Increasing the temperature promoted the generation of pyrolysis gases, with a gas yield of up to 54% at 800 ℃. High temperatures favored the formation of combustible gases such as CO, H2, and CH4 and increased the calorific value of the gases. At 400 ℃, the acid and ester contents in the bio-oil were 27.19% and 33.18%, respectively. Increasing the pyrolysis temperature reduced the ester content and increased the hydrocarbon content, which reached 44.44% at 800 ℃. Because the compositional evolution of DG-derived bio-oil was closely related to pyrolysis temperature, the appropriate temperature should be selected according to the intended application. High-temperature pyrolysis promoted the decomposition of organic functional groups and enhanced the graphitization and aromatization of biochar. These findings indicate that DG-derived biochar has the potential to replace traditional fossil-based materials in energy, environmental, catalytic, and agricultural applications. This study provides a theoretical basis for the directional catalytic pyrolysis of complex DG components to produce high-quality products.