Abstract: Transtensional faults, widely developed in the Pearl River Mouth Basin as links between the deep source rocks and shallow reservoirs, are the key to the analysis of hydrocarbon migration and accumulation. Using 3D seismic and drilling data, the growth process and fault transmissibility for the E18 transtensional fault system in the Enping Sag of the Pearl River Mouth Basin are studied in this paper. With Throw-x profiles, Throw-depth profiles, and fault slip-rate diagrams, the growth process of the E18 fault system in each period is restored for sectional activities of the echelon fault system. Evaluation of hydrocarbon lateral migration across the echelon fault system is also studied according to the characteristics of lithological juxtaposition, shale smearing, internal structure (fault cores), and column height. The results show that the E18 fault system was a single fault in rifting period, with a activity center in the western section. However, during post-rifting dextral strike-slip stage, it became dextral left-step in echelon, having an activity center in the central part. Then, two great vertical migration centers of the E18 fault system are determined, with the maximum activity rate up to 20 m/Ma, corresponding a massive hydrocarbon expulsion period (10 Ma-Now). Finally, it is concluded that the linking sections of the E18 fault system in the Zhuhai Formation and lower Hanjiang Formation are the favorable locations for hydrocarbon lateral migration across the fault surface. Accurate analysis of the E18 fault system would help to understand the formation of E18a and E18f oil fields.