Abstract: To find out the coloring mechanism and the form of water molcule of Guilin hydrothermally-grown synthetic emerald, the test of electronic probe and the test of the spectrum etc are adopted in the research. The result shows that Guilin hydrothermally-grown synthetic emerald is characterized by low content of alkali and Fe but some are out of Cl^-; both I-type and Ⅱ-type water exist. Its color should be attributed to the separation of ⁴F-spectrum term and spectrum term of electrons jumping between the different emerge levels. Moreover, nail-like inclusions of three facies and microwave patterns often exist, which can be regarded as identified features of this kind of emeralds, and FTIR can be applied to identify all kinds of emeralds.