The purpose of the load aggregator（LA）is to provide demand response resources with potential product value and an opportunity to participate in electricity market regulation，make full use of demand-side resources by professional techniques and measures，and provide ancillary services to other market participants.Based on LA researches and experience across the world，an overview on the definition and function of LA is conducted from the perspective of integrating demand response resources.Control resources of LA are classified into three categories，i.e.the adjustable load，the energy storage and distributed generation.Then two key problems are discussed in detail，the operation mechanism，dispatch and control strategy，and the differences between LA and other participants are described.Finally，based on the overview of the existing aggregators and the actual situation in China，measures to promote the business model of LA in China are proposed.