Abstract: There mainly are 5 series of source rocks, including horizons in Upper Tertiary, Upper Cretaceous-Lower Tertiary, Middle-Lower Jurassic, Permo-Carboniferous and Cambrian-Ordovician, in Southwest Depression of the Tarim Basin. The depocenter of Cambrian-Ordovician lay in Awati sag and Tanggubasi sag, in which source rocks with high abundance of organic matter, good types and high maturity were developed. They formed the main source rocks in the depression. Source rocks in Permo-Carboniferous are characterized by wide distribution, varying in abundance and type of organic matter, middle to high maturity. The Jurassic and Lower Tertiary source rocks were mainly distributed in Kasi sag and the southwest margin of the depression, and the Upper Tertiary ones in the mountain front of Yecheng sag.