Successive, steady-state flow and cyclic(episodic), transient flow were two types of fluid flow in sedimentary basins. Episodic fluid flow resulted from the cyclic fracturing or cyclic opening of existing faults and fractures caused by pressure and stress build-up. Episodic petroleum accumulation was processes of the multi stage injections of mixed phase, non-continuous fluids composed of hydrocarbons and water in sedimentary basins. Traps near the top surface of the overpressured systems and traps associated with diapirs and faults were favorable places for episodic petroleum accumulation. Compared with petroleum accumulation through steady-state, continuous flow, episodic accumulation was much faster, and large and medium-sized oil/gas fields could be filled within geologically short period of time. As a result, young traps in which commercial reservoirs could not formed based on traditional model, could become effective exploration target. The main characteristics of episodic fluid flow and petroleum accumulation were non-continuity of the fluid composition and flow processes, rapid changes in temperature and pressure during fluid flow and the multi stage and cyclic nature of fluid flow. The compositional heterogeneities of fluids both in space and in time, the transient temperature response of fluid flow, and the migration fractionation as well as the interaction among multi stage fluids reflected by migration fractionation were effective distinguishing markers for episodic petroleum accumulation.