Abstract: The Koktokay No.3 Li-Be-Ta-Nb-Cs bearing pegmatite dyke of the Upper Paleozoic age is located in the Altai Caledonian-Hercynian fold be lt, Xinjiang Autonomous Region, China. It consists of two major parts: a gent ly dipping “plate”, and a steeply dipping cupola protruding from the plate upw ards. The overall shape of the dyke looks like a solid hat. 　　The Koktokay pegmatite cupola is emplaced in the amphibolitized gabbro and chara cterized by a well developed internal zonal structure. From the border wall inw ards the following 9 mineralogical-textural zones can be subdivided: Ⅰ. Graphi c and pseudo-graphic pegmatite zone; Ⅱ. Saccharoidal albite zone; Ⅲ. Block y alkali feldspar zone; Ⅳ. Muscovite-quartz zone; Ⅴ. Cleavelandite-spodumene zone; Ⅵ. Quartz-spodumene (-cleavelandite) zone; Ⅶ. Thin sliced albite-mus covite zone; Ⅷ. Lepidolite-thin sliced albite (-pollucite) zone; Ⅸ. Blocky quartz and microcline core. 　　Studies on the melt inclusions, fluid-melt inclusions and fluid inclusions in t he minerals of pegmatite provide important clues in judging the magmatic-hydr ot hermal evolution history for the pegmatite formation. The quartz, microcline, g arnet and beryl from zones Ⅰ and Ⅲ contain melt inclusions which are homogeni zed at the temperature range of 610℃～900℃. The spodumene, beryl and quartz f rom zones Ⅳ-Ⅶ contain fluid-melt inclusions and fluid inclusions. The cryst al phases in the fluid-melt inclusions comprise albite, quartz, spodumene, bery l and pollucite etc. The coexisting fluid inclusions in these minerals are of H 2O-CO2-NaCl character, with Th of 310℃～420℃. The salinities are high (wi th NaCl and/or KCl　crystal) or moderate (10%～18%). The quartz from core zone contains only fluid inclusions, with Th of 300℃～320℃ and salinities of 5%～12 %. All above-mentioned temperature measurements are not pressure corrected. T he formation pressures are estimated as 3.2～1.5kb. 　　Based on the zonal distribution and textural relationship of mineral assemblages , multiple generations of rock-forming and rare-metal minerals, as well as the features of inclusions and their thermometric data etc， it is interpreted that the zones Ⅰ, Ⅲ and partly Ⅱ、Ⅳ were crystallized from the volatile-undersa turated silicate melt; zones Ⅴ, Ⅵ and Ⅶ were crystallized from the volati le-oversaturated rare metal-rich residual silicate melt at the magmatic-hydro thermal transition stage where the residual melt phase, silicate crystal ph ase and exsolved fluid phase coexist. The blocky quartz and microcline of zone Ⅸ might be directly crystallized from the high temperature supercritical hydrot hermal solution enriched in silicate solute. The zone Ⅷ and partly zones Ⅱ an d Ⅳ might be considered as metasomatic units. However, the metasomatizing hydrothermal solutions were derived from the pegmatitic residual magma system i tself during its crystallization and evolution, but not from the outside environ ment.