Abstract: Abstract:The influences of floatable oil, chemical oxygen demand (COD_Cr), sugar and volatile fatty acids (VFA) from kitchen waste (KW) liquid substances transformation under hydrothermal pretreatments were investigated using an orthogonal experiment. The orthogonal experiments for three factors and four levels were conducted under different temperatures (80,0, 150 and 200 ℃), heating intervals (40,0, 60 and 70 min) and water addition amounts (40%, 60%, 80% and 100%). The results showed that the floatable oil content was improved significantly after hydrothermal pretreatment. The highest floatable oil content was 67.7 mL/kg at 150 ℃, 40%, 60 min hydrothermal condition, which was 2.65 times higher than the control. In addition, the maximum concentrations of reduced sugar and total sugar were obtained, which increased 16.29% and 38.92% respectively, compared with the control group. As temperature and heating interval increased, the maximum level of COD_Cr was 109.729 g/L at 200 ℃, 40%, 70 min hydrothermal condition, which was 1.39 times higher than the control. The VFA concentration was enhanced substantially, with the highest VFA concentration observed under 200 ℃, 100%, 40 min hydrothermal condition, which increased 66.26% compared to the control. In the liquid phase of KW, the acetic acid and butyric acid concentrations increased, while the ethanol concentration decreased after hydrothermal pretreatment. Variance and poor comprehensive analysis showed that the master factor affecting the liquid substances transformation of KW was temperature, followed by water addition amount and heating intervals.