The Pearl River Mouth basin experienced a transition from rifting stage to depression stage. The synsedimentary strata recorded the tectonic transformation and sedimentary evolution process, thus providing the possibility of determining the fault- depression transformation interface. The characteristics of seismic reflection and sedimentary cycles were used to identify the T72 unconformity that is widely recognized as a traceable and comparable tectono- sedimentary transitional unconformity in the Lufeng south area, and is also the interface to distinguish the upper and lower Enping Formation. Through comprehensive analysis of detrital zircon U- Pb dating, heavy mineral composition and element analysis of sediment in the upper and lower Enping Formation of well LFA, it was proposed that the provenance system of the upper and lower Enping Formation had changed. Combined with the regional sedimentary filling characteristics, it shows that the T72 unconformity in the southern Lufeng area is a fault- depression transformation interface. The study shows that the lake basin inherited the characteristics of the Wenchang rifting lake basin during the deposition period of the lower Enping Formation, with relatively deepwater, and provenance was mainly local and Mesozoic igneous rock basement inside the basin. Sedimentary sequence was obviously controlled by the lower uplifts inside the basin and faults around them, and the proximal braided river delta sandbodies which were distributed around the low uplift in the basin. The well LFA area mainly received the provenance from the Huilu low uplift. During the deposition period of the upper Enping Formation, when lake basin was in the fault- depression transformation period, the lake basin was large with shallow water.Fault activities around the lower uplifts inside the basin were obviously weakened and depositional sequence overlapped toward low uplifts inside the basin. As the supply of Archean to Paleozoic provenance components from outside the basin continued to strengthen, the proximal delta sand bodies transformed gradually to distal braided river deltas and bodies, and at the same time, a broad shore shallow lake environment was developed. The Huilu low uplift was inundated by water, and the well LFA area received sediment from the source outside the northern uplift belt.