Abstract: The activated carbon with hierarchical porous structure was prepared by flash pyrolysis method under differ- ent temperatures(500,800 and 1 000 ℃ ) and residence times(10 and 40 min). The apparent morphology,pore size and carbon structure parameters of chars were obtained by SEM(scanning electron microscope),nitrogen adsorption, XRD(X-ray diffraction) and Raman spectroscopy,respectively. The mechanism on the carbon loss and pore formation of two chars was illustrated by comparing the structural change of chars produced by flash and slow pyrolysis during activation. Results show that the flash pyrolysis temperature controls the formation of mesoporous,and the residence time has an importance on the change of morphology and spatial structure of microcrystalline. The char( M800-10) produced by slow pyrolysis has the specific surface area ( SBET) of 663. 19 m2 / g and the microporous volume of 0． 246 m3 / g at a burn-off of 53． 6% ,meanwhile,its surface has been burned severely. The char( K800-40) produced by flash pyrolysis has the SBET of 859. 14 m2 / g and the microporous volume of 0. 34 m3 / g at a burn-off of 25. 2% , it already has the obvious micro-mesoporous hierarchical structure and no apparent carbon loss outside of the particles. The precursor char prepared by flash pyrolysis under optimal conditions can eliminate the inner diffusion resistance of the activated gas and the activation product. A large number of micropores are developed from the external and internal particles simultaneously,which results in the reduction of carbon loss on particles surface and the cost of activated car- bon.