In view of long heat preservation time of ammunition, in order to gain accurate time to condition fullness, the experiment study of heat preservation time of ammunition was carried out. In the paper, the process of the ammunition's temperature conditioning was analyzed based on the theory of transmit heat. The model of heat preservation of ammunition was established. The relation of the distribution of ammunition's temperature field with the time of heat preservation and the time of heat preservation were got. The result approves the time of the ammunition temperature conditioning can be compressed a lot. The study provides scientific basis for improvement.