Abstract: The Lower Carboniferous in drills of the northern part of Tarim Basin can be divided into three forastions from top to bottom: Yangbaxi, Kalashayi an Bachu. Abunbant foraminiferal and fusulinid fossils occur in Yangbaxi and Kalashayi formation. Fusulinid fossit amounting up to 4 genera and 18species belongs' to Eostaffella zone. Foraminferal fossil containins up to 25 genera and near 60 species could be categorizedas two assemblages: 2. Endothyranopsis cassus——Archaediscus krestovnikovi; and 1. Endothyra inflataf minima——Archaesphaera minima. The geological age of both fusulinid zone and 2 foraminiferal assemblage is from middle-late Visena to early namuran, and that of 1 foraminiferal assemblage is middle Tournaisian.