We introduce a nove method of measuring fluorine atom flow rate which named titration-HF absorption method. It uses discharge driven single-line HF laser as detect light source, monitors the absorption of titration product-HF molecule, and gets the relationship between F atom flow rate and titration gas (hydrogen gas) flow rate. By this method, in the condition of different NF3 flow rates and different spectra lines, the fluorine atom flow rate of a discharge driven HF/DF chemical laser is measured. It is found that the absorption of lower rotational state line is stronger, and about 1.0～1.1 fluorine atom can be dissociated from one NF3 molecule we analyze the relationship between the transmittance and the fluorine atom flow rate along with the temperature. The factors that influence the measuring precision are also analyzed and the countermeasures are given for the future work. Experiment results prove that the titration-HF absorption method is a simple, useful method of fluorine atom flow rate measuring.