Abstract: Using a batch autoclave，preliminary study was made on the reaction of coal tar in supercritical water. Attention was centered on the influence of temperature, residence time and density of water on both composition and yield of products. Experiments were performed between 390 ℃～480 ℃, solvent density 0.32 g/cm3～0.44 g/cm3, and reaction time up to 80 min. Compared with the traditional pyrolysis of coal tar under normal pressure or high pressure, it is found that during the upgrading of coal tar in SCW, light oil is increased at the expense of gas and coke products, probably due to the cage effect of SCW in the pyrolysis of coal tar. SCW may be an ideal medium for upgrading of coal tar and can suppress gas formation and coking of coal tar. In order to get light oil as much as possible, the optimal conditions are: temperature 450 ℃, density of water 0.40 g/cm3 and residence time 20 min. The yield of light oil (HS) is 51.55w% under these conditions, 30％ higher compared with that in the raw material.