With the purpose of studying the effect of preservation time to the extraction of genomic DNA from A. Trifoliate, the genome DNA was isolated by improved CTAB method with the leaves that preserved for one month and six months under low temperature respectively. The quality of the DNA was examined with agarose gel electrophocesis and ultraviolet sepectrophotometer. The results showed the high quality DNA was extracted from the leaves that preserved for one month, which could be used for the next study. So the leaf would disintegrate if preserved for too long a time, and the extraction of DNA would be affected.