Abstract:  The pyrolysis experiments of oil shale from Liushuhe were performed by using an autoclave with saturated or unsaturated water. The formation mechanism of pyrolysate including retorting gas, oil and bitumen was discussed. It is found that the free radical and carbocation reactions occur simultanously during oil shale pyrolysis. The physical and chemical properties of water at high pressure and temperature are very different from those at normal temperature and pressure, which can promote the carbocation reaction of oil shale as the acid and alkali catalyst. At the same time, the free radical reaction also occurs because of the diversity in chemical bonds of oil shale.