The results of experimental and theoretical study on population inversion in the He-like Al ions are presented for the pumping laser intensity range of ～2×1014W|cm2. The effects of different target structure (foil, plane and half-cylinder) on the 2p-3d population inversion of the He-like Al ions (45nm) in a spot focused laser plasma have been studied experimentally. The plasma parameters such as electron temperature, electron density and the ratio of H-like ion density to He-like ion density, are diagnosed by spectroscopic methods. Results are compared with C-R model calculations.