Activated carbons were prepared through oiltea shell heat decomposition under vacuum condition using zinc chloride as activating reagent.The factors affecting the adsorption properties of activated carbons were studied, including the concentration of zinc chloride, system pressure, activation time and activation temperatures. Surface area and porosity characteristics were determined with the analysis of N2 adsorption-desorption isotherms. The functional groups on the surface were analyzed by FT-IR spectroscopy. Microstructure of the sample was examined with scanning electron microscopy. The results show that the optimized condition for the preparation of activated carbon is as follows: zinc chloride concentration of 60%，immerse ration of 1:3, system pressure of 50kPa, activation temperature of 450℃ and activation time of 1h．The iodine absorption value and methylene blue absorption value of the prepared activated carbon are 1120 mg•g-1 and 373.16mg•g-1, respectively．The surface area is 2023.15 m2•g-1and total porous volume is 2.34 cm3•g-1 with an average porous diameter of 4.63 nm. The activated carbons prepared under vacuum condition have good absorption performance.