The chemical hydride NaMgH3 is considered to be a promising candidate for hydrogen storage materials with its high hydrogen gravimetric and volumetric densities. The mechanism of the improved dehydrogenating properties of NaMgH3 doped by F anion was investigated using plane-wave pseudopotential （PW-PP） approach based on the density functional theory （DFT）. Computational results show that the formation enthalpy and reaction enthalpy of the hydride decrease drastically with the substitution of F for H. This results in a favorable thermodynamic modification, and facilitates the dehydrogenation reaction of the hydrides.