The effects of several sugars (glucose, maltose and sucrose), polyols (glycerol, ethanol and sorbitol) and surfactants (tween 20 and span 20) on thermostability of nicotinamide adenine dinucleotide (NAD) kinase were studied. In addition, a composite protective additive was obtained by the orthogonal experiment and its effects on the thermostability, optimum reaction temperature, optimum pH and storage stability of NAD kinase were also investigated. The results showed that maltose, glycerol, ethanol, and tween 20 could improve the thermostability of NAD kinase significantly. The obtained composite protective additive included mass fraction of maltose 0.6%, volume fraction of glycerol 8%, volume fraction of ethanol 8%, and volume fraction of tween 20 0.6%. After treatment of the composite protective additive, at 55℃, the half-life of NAD kinase was increased by 16.7 times, and it increased from 1.1 h to 18.4 h. Meanwhile, the optimum reaction temperature increased from 35℃ to 50℃, the range of pH stability expanded from 6.5～9 to 5.5～9.5. The retention of enzyme activity was an improvement of 31% at 4℃ storage for 28 d.