Abstract: Using the t ight- binding theory, the influences of the thermal expansion on the energy band structure of the solid with a body- centered cubic lattice was discussed, the 1S and 2S energy bands of body- centered cubic lattice were calculated. The results show that with the increase of temperature, the thermal expansion makes lattice constant change, which will result in the shifts of the center of the 1S and 2S energy bands and the energy band edge; therefore,
the width of every energy band and the forbidden band- width between two bands will change.These results can explain fairly the partial experimental results of the Li metal.

Key words:  , thermal expansion, energy band- width, forbidden band- width