The laser induced iodine fluorescence(LIIF) is an advanced technology to visualize the flowfield. To get the precision of using this method to investigate the mixed performance of the nozzle in chemical lasers, the cold flowfield of HYLTE nozzle in CW DF/HF chemical laser is simulated. The flowfield which uses the mixed gas made up of helium and iodine as the oxidant, the helium gas used as fuel is measured. The distribution of the mole fraction of the F atom in the first flowfield and the I₂ molecular in the second flowfield are compared. When the mass fraction of iodine molecular in the He-I₂ mixed gas is about 54%, using LIIF to measure the mixed mechanism of HTLTE nozzle in DF/HF chemical laser is more precise.