We have developed a three-dimensional electron-photon Monte Carlo transmission (MCT) code. The conversiontransmissivity coefficient of hot electron x-ray, ηet, is analysed theoretically and simulated numerically using the MCT code. Experiments of disc and cylindrical targets have been performed at the Shenguang-Ⅱ laser facility.A multi-channel filter-fluorescence spectrometer was used to obtain the hard x-ray spectrum. The temperature and energy of hot electrons are induced from the hard x-ray spectrum and the ηct value. The average energy fraction of hot electrons is 14% of incident laser energy for the 1ωNd laser and the spherical target with an average temperature of hot electrons of 36 keV, while it is 15% for the 1ω Nd laser and the cavity target with an average temperature of 54keV. We have also obtained the results of 5.6% and 13.3 keV for the 3ωNd laser and the disc target, 4.9% and 17.9keV for the 3ωNd laser and the half cavity target with a thin wall, and 2.1% and 22.4keV for those with a thick wall. The experimental results agree with theory and simulation.