This study focuses on the palaeoecology of the Late Devonian ostracods based on more than 4,500 carapaces and valves collected from stratal sections in western Junggar, NW China. According to the ostracod faunas from the Hongguleleng Formation, 3 ecological assemblages are proposed for open oceanic island arc context, that is, Ostracod Assemblage-1, Ostracod Assemblage-2, and Ostracod Assemblage-3. They characterize the foreshore, nearshore, and offshore environments, respectively. The water energy should be the first environmental factor controlling the composition of the ostracod assemblages from the Lower Member of the Hongguleleng Formation, and salinity fluctuations could be also involved.