A four-species 1-D hybrid numerical model was set up to simulate the process of formation of large-dimension plasma produced by injecting electron beams into air. It showed that plasma of the order of 0.5m in length and 1012cm-3 in density can be produced by an electron beam with the energy of 140keV and flux of 50mA/cm2. The effect of space charge associated with the beam on the beam propagation and related process vanishes soon after the plasma is produced. The beam flux is directly relevant to the plasma density, but the beam energy affects both the dimensions and the density of produced plasma.