Structure of bio-oil and residue obtained from the thermochemical liquefaction of straw by hot compressed water was investigated. The products were obtained by sampling during the experiment period at the temperature of 200, 220, 250, 300, and 310 degrees C. The products of liquefaction were separated into water-solution fraction, tetrahydrofuran solubles (bio-oil), and insolubles (residues). The raw straw and residues were analyzed by scanning electron microscopy (SEM), Fourier transform infrared (FTIR), and elemental analysis. The bio-oil and water-soluble products were analyzed by GC/MS and TOC, respectively. The results suggest that the main component including cellulose and hemicellulose of straw began to decompose at 200 degrees C, but the lignin decomposed at 250-300 degrees C. The main compounds of bio-oil were butylated hydroxytoluene and dibutyl phthalate; some high molecular compounds were produced by further repolymerization as the temperature increased. The results might be helpful to investigate the product characteristics at different temperatures during straw liquefaction and also establish pathways of the straw liquefaction, which can be utilized to improve the yield of goal products (bio-oil, phenols, and other useful chemicals).