In recent years，there has been no significant breakthrough in the exploration of Sangonghe Formation in the west sag of Well Pen-1 and its periphery in Junggar Basin. The analysis shows that the insufficient understanding of the favorable reservoir distribution rules restricts the exploration process in this area. Based on the previous research work and the core，logging and seismic data，the palaeogeomorphology before sedimentation of Sangonghe Formation is restored. Then，the geological characteristics of deep-water sediments are systematically analyzed，and the control of paleogeomorphology on the sedimentary system is summarized. The results show that the typical deep-water sandy debris flow deposit is developed in Sangonghe Formation of the central area in the west sag of Well Pen-1，there are thick-massive sandstones with floating mud-gravel and argillaceous tear debris in the reservoir，and the top/bottom abrupt contacts are common. Four sedimentary units，such as underwater low uplift，underwater gully，slope and deep-water sag are developed before sedimentation of Sangonghe Formation. Two-stage slope break zones in the slope area，which obviously controls the sedimentary system. There are two-stage slope break zones in the slope area，which obviously control the sedimentary system and by which the research area is divided into shallow-water delta front，prodelta，and shallow lake-semi-deep lake facies. The sandy debris flow is developed in the shallow lake-semi-deep lake sedimentary zone in the west of M17-QS1. The exploration practice has proved that the sandy debris flow reservoirs have good physical properties，a relatively large oil and gas reservoir can be formed in the case of good oil and gas source and matching conditions，which is the best field for exploration prospect of“lower sag”in the west sag of Well Pen-1.