According to the Wiener-Khintohine law, we have derived a general formula on the temporal coherence of gas laser with multi-longitudinal modes, and given results on the temporal coherence of gas laser under the state of symmetric and nonsymmetrio distribution, When (1) . It is consistent with the results of reference [4] and [2-3] respectively. Finally, from the theory and experiment, this paper analyses and studies temporal coherence of the above-mentioned four cases.