The construction of virtual power plant (VPP） is now in the ascendant. It is necessary to comprehensively consider the economic requirements of VPP operators and the safety requirements of power grid for the participation of virtual power plants in grid dispatching. However, under the current power system information security requirements, the market-oriented virtual power plant operators have no aceess to the grid topology and real-time power flow information, and it may bring serious security risks to the power grid with the increase of aggregated resources in VPPs. The definition of virtual power unit is put forward based on the current situation of power dispatching system in China. Moreover, a dispatching architecture with partition aggregation and hierarchical scheduling for market-oriented VPPs is prospected from the aspects of partitional aggregation construction method of virtual power units, multi-level scheduling mode for VPPs and way of VPPs participating in the power market. Finally, an example shows that the dispatching architecture proposed can support the VPPs to participate in power grid dispatching and market transactions safely and economically without the grid topology information.