In this paper, by analyzing the principle of the Grid-controlled Modulated X-ray Source, the core structure parameters including half width of the cathode notch, depth of the sinking filament and target angle are systematically designed and optimized. The electron-photon conversion efficiency and the minimum cut-off voltage of the X-ray source are calculated. In addition, an experimental system is built for the optimized GMXS test and ground X-ray communication (XCOM) verification. The experimental results indicate that with the same anode voltage and filament current, the number of emitted photons increases by 16-18% after optimization, the output X-ray photons intensity stability is better than +/- 1.4%, and the cut-off voltage is reduced to -10 V. Based on this optimized GMXS, the ground XCOM rate increased to higher than 1 Mbps.