A robust, direct, rapid and non-destructive X-ray diffraction crystallography method for detecting the Tibetan medicine Zuotai is presented. Powder samples of Zuotai, cinnabar and calomel were unambiguously characterized using powder X-ray diffractometry (PXRD) by comparing a practical identification of metacinnabar in the analyzed material, which confirmed the present of metacinnabar in Zuotai. At the same time, 11 strong lines in the fingerprint of Zuotai were selected to indicate the effective constituents of Zuotai, which were listed in the form of d-( I/I0 )%: metacinnabar 3.356 4/100, 2.061 4/55.0, 2.911 8/35.0, 1.760 1/37.0, 1.339 5/12.0, 1.304 5/10.0, 1.192 0/10.0, 1.683 4/7.0, 1.458 0/5.6. sulfur 3.824 4/100, 3.197 5/40.2, 3.442 2/38.1, 3.095 6/19.7, 5.690 9/16.8, 2.851 0/16.3, 2.414 4/11.3. The results showed that mercury chemical state is metacinnabar with sulfur in Tibetan medicine Zuotai. This method should be supplemented to quality control of rare traditonal Chinese medicine.