Averaging principle is an effective method for investigating dynamical systems with highly oscillating components. Under suitable conditions, the fast variable can be “averaged out” to produce an averaged system, which is easier for analysis and governs the evolution over a long time scale. In this talk, we establish the averaging principle for monotone SDEs and singular SDEs respectively. This talk is based on joint works with Zimo Hao, Zhenxin Liu, Michael Röckner and Xicheng Zhang.