Effects of focusing conditions on femtosecond laser induced plasma fluorescence in air are investigated by using different focal length lenses. Under the tightly focusing condition, the fluorescence spectra are composed mainly of continuous spectrum and line spectra from N and O atoms, which is due to the higher laser intensity and corresponding higher electron density than those in the case of weakly focused laser beam. In the latter case, only line spectra from air molecules are observed. Besides, the intensity of line spectrum as a function of propagation distance is measured, which reveals the evolution of the plasma filaments.