The I-V curves of a series of possible models of Cs/C(0001)—(2×2) surface are calculated by dynamical LEED theory with RSP and RFS methods. The dalculated curves are selected with experimental results and the best structure is chosen by R-factor calculation. The model of Cs intercalating graphite layers forming intercalate structure and the model of Cs atoms adsorbed on top position of graphite surface are ruled out by R-factor examination. The most probable structure is that Cs atoms adsorbed on hollow position of graphite layer with a interlayer distance of 2.80 ? between Cs laver and graphite, and substrate has the same, structure as that of graphite bulk structure.