The effect of two-level pretreatment on the slow/fast pyrolysis characteristics of water hyacinth were studied. The water/acid wash had the significant effect on remove the sulfur, nitrogen and ash, which can greatly improve the quality of pyrolysis products. water/acid wash had negative impact on the heavy oil in the hydrothermal system. The heavy oil yield of the Hy-R, Hy-W and Hy-A were 37.24%, 25.70% and 27.06 wow %, respectively. Among all the pretreatments, except for K element, all the detected heavy metals (Al, As, Cr, Cu, Mn, Ni and Zn) accumulated. In addition, the CPI of Tr-R, and Tr-W and Tr- A were -23.91, -13.93 and -18.85 x (10(-7)/(min(2) x degrees C-3) which were much larger than that of Hy-R, Hy-W and Hy-A (-2.99,-6.60 and -9.26 x (10(-7)/(min(2) x degrees C-3)). The absorbance of NH3, HCN, C=O, CO, CO2, CH4 and H2O were detected in slow pyrolysis. The pyrolysis effectiveness index of Hy-R reached the largest value of 0.375. The volatiles of fast pyrolysis were divided into fourteen groups, including CO2, alcohols, acids, phenols, aromatic hydrocarbons, esters, aldehydes, ketones, aliphatic & alicyclic hydrocarbons, nitrogen containing compounds, organo-sulfur compounds, sugars, ethers, furans to present the compositions of the pyrolysis vapors. (C) 2019 Elsevier Ltd. All rights reserved.