A background elimination method based on harmonic detection in no absorption spectral region (HDINASR) is proposed. It can be used in open and closed gas detection based on tunable diode laser absorption spectroscopy (TDLAS). Background signal component is discussed, background signal searching and spectral line selection principle are designed, and the minimum wavelength spacing formula between adjacent absorption spectral lines is given. The experiment is designed to detect hydrogen fluoride (HF) using TDLAS experimental system. The HF target absorption spectral line, laser working temperature and temperature range of background searching are determined. Experimental results show that with the application of HDINASR background elimination, the curve correlation is increased by 3.4% and the relative amplitude of volume fraction accuracy improving is increased by 5.8%. HDINASR provides an effective background elimination method for open and closed gas detection.