Abstract: Boundary slip is a long-standing scientific problem in the research of fluid mechanics, and is a highly attractive issue in micro/nanofluidics. Recently, the research community has gradually reached a consensus on the slip length of simple liquid (such as water) on smooth liquid-solid interface. However, the slip of complex fluids on liquid-solid interface has become an emerging and attractive issue. Therefore, this paper reviews the new experimental results and theoretical descriptions obtained in the research progress from the simple liquid to complex fluids. In particular, we mainly introduce how to understand the slip of complex fluids on the liquid-solid interface and its impacts, based on the recent experimental results in polyelectrolyte solutions from Prof. Charlaix's group using surface force apparatus.