Working conditions of chemical lasers are discussed. The particle number concentration changing with the J values is shown. There are quantum number J0 of cutoff wavelength and quantum number Jm of maximum spectral transition. The method of working status diagnosis of chemical lasers is proposed by combination of spectrum measuring, the relationships between J0, Jm, cavity static temperature T, and the mass fraction ratio of lower level and upper level Nx. The cavity static temperature T and mass fraction ratio of lower level and upper level Nx according with the actual spectrum measurements of HF chemical laser are given.