Abstract: Flow past louvers is common in engineering applications. Self-sustained oscillations caused by the flow configuration lead to periodical pressure fluctuations. Because of that, periodic loads will be applied on circumambient structures continuously and may give rise to fatigue problems. Using a numerical simulation method, self-sustained oscillations caused by flow past a louver are studied in this paper. The numerical results show that when the Mach number is small, the self-sustained oscillations belong to a pure fluid dynamic problem. This phenomenon is induced by generation and propagation of large-scale vortices which are generated from fluctuations of the shear layer. In addition, pressure oscillations generated by this phenomenon contain two significant features:sustainability and periodicity. The frequency of the self-sustained oscillations is spatially uniform. Along the mainstream direction, the amplitude of the self-sustained oscillations sharply increases first and then stabilizes. At the impingement edge, it slightly decreases. With an increasing size of the cavity inside the louver, the variation of the frequency basically remains stable. On the other hand, the amplitude increases gradually and remains stable when the cavity size reaches a critical value.