Biyang Depression was in the stage of transition from fault depression to down-warping depression during the sedimentary time of the Member 2 of Hetaoyuan Formation. Sedimentary environment and its evolution, distribution of sedimentary facies and sand bodies are discussed on the base of the data of log, drilling and C, O isotope. Five sedimentary systems, i. e., braided river delta, fan delta, delta, inshore subaqueous fan and saline lake, were distinguished in member 2 of Hetaoyuan formation, Biyang depression. The properties and distributions of the sedimentary system are controlled by paleotopography and supplying condition of sediments. There exits fan delta sedimentary system in the west and middle of the steep slope, while inshore subaqueous fan in the east. There is braided river delta sedimentary system in the northeast of the gentle slope, while delta in the northwest. According to the calculation from the data of C, O isotope, the average paleowater temperature is 28.17 ℃, and the average paleosalinity index is 126.84, indicating its saline setting. In addition, two depositional cycles are shown according to the evolution of δ¹³C、δ¹⁸O、Z and t. The first cycle is from the bottom of Member 2 of Hetaoyuan Formation to the bottom of third sand group, and the second is from the bottom of third sand group to the top of Member 2 of Hetaoyuan Formation.