Abstract: A method for determination of 5 monosaccharide compounds, including mannose, glucose, galactose, xylose, and arabinose in deep roasted coffee powder by high performance liquid chromatography with pre-column derivatization was proposed, and orthogonal partial least squares-discriminant analysis (OPLS-DA) was combined to identify whether deep roasted coffee powder was adulterated with different proportions of other substances. Green coffee beans and adulterants were deeply roasted, ground, sieved, and mixed at different mass ratios to make simulated samples. 1.000 0 g of the simulated sample was taken and placed into a 50 mL-centrifuge tube, and 10 mL of 1 mol · L⁻¹ hydrochloric acid solution was added. The mixture was homogenized and hydrolyzed at 90 ℃ for 2.0 h. After cooling, the pH of the solution was adjusted to 7.0 with 5 mol · L⁻¹ sodium hydroxide solution, and the volume was made up to 20 mL with water. Subsequently, 200 μL of the solution was transferred to a 5 mL-centrifuge tube, and 200 μL of 0.3 mol · L⁻¹ sodium hydroxide solution was added. The mixture was mixed well, and 200 μL of 0.5 mol · L⁻¹ 1-phenyl-3-methyl-5-pyrazolinone solution was added. The solution was vortexed for 1 min and derivatized at 70 ℃ for 100 min. After cooling, 200 μL of 0.3 mol · L⁻¹ hydrochloric acid solution was added and vortexed, and 1 mL of chloroform was added for extraction, and the mixture was centrifuged for 5 min. The lower layer was discarded, and the extraction was repeated three times. The upper layer was filtered through a 0.22 μm filter membrane, and 5 monosaccharide compounds in the filtrate were determined. An Eclipse plus C₁₈ chromatographic column was used as the stationary phase, and isocratic elution was performed with acetonitrile-0.1 mol ·L₋₁ sodium phosphate buffer (pH 6.7) at a volume ratio of 17∶83 as the mobile phase. As shown by the results, linear relationships between the corresponding derivative peak areas and mass concentrations of 5 monosaccharide compounds were found in the range of 1.0-500 mg · L⁻¹, with detection limits (3S/N) in the range of 0.03-0.55 mg · kg⁻¹. Test for recovery was made by the standard addition method, giving results in the range of 83.1%-121%, with RSDs (n=6) of the determined values less than 3.0%. The OPLS-DA model was used to identify whether the deep roasted coffee powder samples were adulterated. Three differential components with significant contributions, including mannose, arabinose, and glucose were screened out by the variable importance in projection values.