Abstract: A criterion for the intercalation of a metal chloride in a molten state into graphite was proposed based on the thermodynamics of the intercalation reaction and chemical band theory. The valence electronegativity of element and ionic potential are taken as the chemical band parameters and a band parameter function λ is defined as a criterion to select a guest metal chloride to prepare a graphite intercalation compound (GIC). The ability of a metal chloride to be intercalated into graphite and the stability of the resulting GIC are estimated. The results show that GICs synthesized at a temperature lower than 700 ℃ are more stable when a metal chloride is chosen from the region of λ≤1.2. A metal chloride with λ between 1.2 and 1.8 cannot be easily intercalated into graphite alone. The metal chlorides with λ≥1.8, most of which are alkaline earth chlorides or alkali metal chlorides, are not appropriate as guests to prepare GICs by a molten salt method. The criterion is consistent with the experimental data and some new expected results are also obtained.