We measure the Cu 2p X-ray photoemission spectrum (XPS) of Sr2CuO3 andanalyze it by means of exact diagonalization calculations for(CunO3n)4n- clusters.In Sr2CuO3, the intensity ratio of the 3d9 satellite to the 3d10 Lmain line is 0.35–0.4, which is evidently smaller than that in the otherhigh-T c related cuprates. We ascribe it as the smaller charge-transferenergy between the Cu 3d and O 2p.The origin of the broad main-line of Sr2CuO3 is also discussed.