In the context of energy structure transformation, the penetration of distributed energy resources in power systems is gradually increasing, and the distribution network is no longer a simple passive network, resulting in closer interaction between transmission and distribution networks. The limitations of the traditional transmission and distribution split energy management mode are prominent. Firstly, this paper summarizes the relevant research results of transmission and distribution co-optimization under vertical monopoly management system from four aspects. Then, aiming at three scenarios including distribution companies participating in the centralized market and distributed energy resource aggregators participating in the centralized market, and distributed energy resources participating in the local market during electricity market reform process, the relevant research results of transmission and distribution co-optimization under market environment are sorted out. Finally, the transmission and distribution co-optimization of power systems with distributed energy resources is summarized and prospected.