Influence of photon absorption of ground state molecules in resonator cavity on HF-DF dual-band chemical laser output performance is investigated through experiments. Variations of spectra and output powers of HF laser and DF laser operated with different positions of H2/D2 injection are measured and analyzed. The results show that the spectral lines of 1P (the P-branch transition between vibrational states of ν=1→ν=0) are absorbed by the ground state molecules through the mechanism of single-photon resonance absorption. The spectral lines of 2P (the P-branch transition of ν=2→ν=1) are absorbed by the ground state molecules through the mechanism of double-photon resonance absorption one by one. Cascading transition effect of lasing band between vibration-rotational states exists in some extent. Output power of HF laser decreases by approximately 50%, and output power of DF laser decreases by approximately 90% when the amount of ground state molecules and the amount of excited state molecules are equivalent. Traditional fuel compositions are not applicable for developing combustor-driven HF-DF dual-band chemical lasers.