The influence of NCl(a1Δ) self-annihilation on the energy extraction of NCl(a1Δ)/I laser at 300 K has been simulated using a simplified continuous flow Farby-Perot (F-P) resonator model. The results show that NCl(a1Δ) self-annihilation has an important effect on the location of the cavity resonator, the profile of power density along the flow direction and the total power. The optimal location range of the cavity resonator is dramatically shorten with NCl(a1Δ) self-annihilation. The available power with NCl(a1Δ) self-quenching is much less than that obtained without NCl(a1Δ) self-annihilation at small initial density of HI but has little difference at large initial density of HI.