The invention relates to the field of power dispatching, and provides a power grid dispatching system and a power grid dispatching method. The power grid dispatching system comprises a power grid coordination dispatching system and at least one energy management system which are connected with each other, and the energy management system is configured to determine power plant overall external characteristic data of a power plant where the energy management system is located and transmit the power plant overall external characteristic data to the power grid coordination dispatching system; thepower grid coordinated dispatching system is configured to optimize the generated power of a generator set of the power plant where the energy management system is located according to the overall external characteristic data of the power plant and feed back a dispatching result to the energy management system; the energy management system is further configured to enable the power plant to operatein an optimal mode according to the scheduling result. According to the system and the method, the overall operation efficiency of the power grid can be maximized at least.