To provide support for the breakthrough in hydrocarbon exploration in the conventional-unconventional transition zone on the southern slope of the Mahu Sag, Junggar Basin, the 3rd Member of the Permian Fengcheng Formation ( P1 f3 ) in the Mahu126 Well Block was taken as the research object. Based on high-precision 3D seismic, well logging and well testing data, integrated well-seismic studies on stratigraphic division, structural interpretation, reservoir prediction and hydrocarbon accumulation characteristics were car- ried out. The results show that misunderstandings exist in the traditional stratigraphic division scheme of the study area, and a complete stratigraphic sequence of the Fengcheng Formation is actually developed. After stratigraphic framework reconstruction, a new strati- graphic division scheme was established, namely “ Upper Permian Upper Urho Formation-Middle Permian Lower Urho Formation-Mid- dle Permian Xiazijie Formation-Middle Permian Fengcheng Formation-Lower Permian Jiamuhe Formation” , which clarifies the pinch- out characteristics of top truncation and bottom onlap in the western onlap-denudation zone. The P1 f3 is overall a southeast-dipping mon- ocline with multi-stage fault systems, forming a structural-lithologic composite trap with an area of 60. 22 km2 . The reservoirs in the P1 f23 submember are tight glutenites deposited by braided channels of fan deltas, characterized by low porosity ( average 9. 69% ) and low permeability ( average 0. 13 mD) . The reservoir space is dominated by intragranular dissolution pores, and the reservoir physical properties present a distribution pattern of favorable in the west and poor in the east. The dual-parameter pre-stack inversion technique of “ low P-wave impedance < 11 000 ( g / cm3 )·( m / s) + low Vp / Vs < 1. 7” was innovatively applied, achieving a 91% coincidence rate in lithology identification and accurately delineating high-quality reservoirs. Guided by this technique, industrial oil flow was obtained from 10 intervals in 9 vertical wells in the study area. During the pilot production of horizontal wells, daily oil production stabi- lized at over 20 t, cumulative oil production reached 2. 08 × 104 t, and the proved oil-bearing area reached 14. 25 km2 . The research re- sults deepen the connotation of the full petroleum system in the Mahu Sag. The established technical system of “ stratigraphic framework reconstruction-dual-parameter reservoir prediction-deployment by zone and interval” and the hydrocarbon accumulation model of “ struc- ture controlling hydrocarbon accumulation and lithology delimiting boundaries” provide key geological understandings and practical ref- erences for hydrocarbon exploration in similar onlap-denudation zones and transition zones, and strongly support the large-scale reserve growth and cost-effective development of hydrocarbons in the Junggar Basin.