The effect of working gas on the output energy stability of a repetitively pulsed HF laser is investigated. The calculated results show that the decomposition of SF6 in the discharge region of the laser is about 1.5%, a little larger than the experimental data. The gas consumption rate is about 2.2×10 15 (cm -3·s -1), and the consumption is 3~4 orders of magnitude smaller than the initial content. The stability of the laser output energy can be improved by properly controlling the HF molecular concentration in the laser chamber and replenishing the working gas at a right time. The change of the laser output energy can be divided into two stages, a transitional stage and a maintenance stage. The transitional stage plays a decisive role in the determination of the output power level of a repetitively pulsed HF laser. The calculated results can provide a technical support for the design of a repetitively pulsed non-chain HF laser.