The influence of the peaking capacitor and the pressure of mixture gas on the performance of UV preionized pulsed HF laser is investigated. There exist an optimum mixing ratio (SF 6/C 2H 6=20∶1) and an optimum capacitor ratio (C p/C s=0.3). In addition, the laser pulse width decreases as the gas pressure increases. Under the optimum mixing ratio the maximum attainable output energy and the optimal pressure increase with increase of the charging voltage. The laser gives laser output energy up to 400 mJ with a maximum electric efficiency about 2.2% and the specific energy 31.7 J/l·atm.