Based on a comprehensive research on several sections of the Hongguleleng Formation in western Junggar, the boundary between the Hongguleleng and Heishantou Formations was proposed at the disappearance of calcareous clastic rocks and the appearance of dark finegrained volcanoclastic rocks. The uppermost part of the Hongguleleng Formation is a suite of clastic rocks (calcareous siltstones with ‘ Lingula ’, tuffaceous sandstones, granule conglomerates, or sandy conglomerates with shellsdeposited in the backshore environment, and is named the “Yangzhuang Sandstone”. The boundary between the two formations can be easily identified and correlated in many stratal sections. Nine genera (or subgenera) and 14 species of trilobites were collected from the upper part of the Hongguleleng Formation and the lower part of the Heishantou Formationincluding Omegopssp. Pudoproetussp. Linguaphillipsia sp. Belgibole sp. B.abruptirhachis Philliboloides sp. , Winterbergia（W. ） sp. , W.（Eowinterbergia） ? sp. , Weberiphillipsia sp. , Conophillipsia sp. 1, C . sp. 2, C . ? sp. 3, C . ? paucicostata , and C . ? morganensis . According to the biostratigraphy of trilobitesthe DevonianCarboniferous boundary was established in western Junggar and is placed between the disappearance level of Omegops and the appearance level of the BelgiboleConophillpsia assemblage zone. The DevonianCarboniferous boundary is in accordance with the boundary between the Hongguleleng and Heishantou Formations. The “Yangzhuang Sandstone” resulted from a sealevel fall event that happened at the end of Devonian in the islandarc context, and is also the embodiment of the Hangenberg event during the DevonianCarboniferous transition in western Junggar.