The high efficiency, high energy operation of an intense electron-beam (e-beam) initiated hydrogen fluoride (HF) chain chemical lasers was theoretically analyzed using a new computer code including both neutral and ionic reactions. The used gas mixture is F2/H2/SF6/02. Both theoretical HF laser output energy and pulsewidth were in good agreement with those of the experiment, respectively. Using this code, we calculated the performance characteristics as a function of e-beam current pulsewidth, H2 partial pressure, initial total gas pressure, and gas temperature. In order to optimize he total gas pressure in terms of laser engineering, we introduced a new parameter which shows the effect of the pressure rise by the exothermic chemical reactions. The optimum total gas pressure of 850 Torr was predicted in our system. Moreover, lowering the initial gas temperature from 300 to 220K both the output energy and the chemical efficiency were found to be improved. In consequence of the experiment based on the theoretical simulation results, a maximum output energy of 5.0kJ(268J/1) was obtained from the low total pressure mixture(282Torr) of F2/H2/SF6/02 = 139/58/45/42 (Torr) with a high electrical efficiency of 284% and a chemical efficiency of 20.3%. Aiming at the achievement of the high chemical efficiency, a maximum chemical efficiency of 29.6% was attained with a 317 Torr mixture of F2/H2/SF6/02 = 167/30/70/50 (Torr). The maximum output energy was 4.9kJ(259J/1), corresponding to an electrical efficiency of 246%.