Beryl crystals occurring in nature are mostly prismatic, tabular ones are rarely observed. This paper presents a study of the structure of a tabular crystal of beryl from the Xuebaoding greisen, and a comparisons with a prismatic crystal sample of beryl from the Altay pegmatite. The beryl of Xuebaoding is rich in Li and Na, containing 0. 71 % of Li2O and 1. 59 % of Na2O. And it has a relatively high c/a ratio of 1. 001. These facts show that the beryl of Xuebaoding belongs to the Na-Li beryl or "tetrahedral" beryl. The data of diffraction intensity of the crystal structure were obtained with the Siemens P4 four-circle diffractometer. The structures were solved by direct methods and were refined to R indices of 2 % - 3 %. The results show that substitution of Be by Li caused the Be-O bond distance to expand. The formation mechanism of the tabular morphology of beryl is also discussed in the paper. The content of and/or chemical form of Si in the ore-forming fluid may be one of the important factors affecting the morphology of beryl crystals.