With the increase of power loads and the integration of new energies

it brings new challenges to the security and economic operation of the power grid. In order to improve the security margin of power grid and optimize the resource allocation within the larger space

it is necessary to tap the potential of power transmission based on existing equipment. Therefore

a basic concept of transmission operation flexible space is proposed to explore the operation flexible space of the transmission line and tie line. This paper proposes two ways to improve transmission operation flexible space and establishes corresponding models: 1)Establishing the short-time capacity-increase model of transmission lines after contingencies based on the power transfer distribution factor; 2)Establishing the adjustable flexibility model of the tie line that considers operational constraints of the external network based on external static equivalent model. Furthermore

the economic dispatch with N-1 security model considering transmission flexible space is proposed. Finally

the benefits of transmission operation flexible space are evaluated through the IEEE 30-bus and IEEE 9-bus interconnected system. Simulation results show that the dispatch method considering transmission operation flexible space can improve the wind power consumption and reduce the operation cost effectively compared with conventional dispatch methods.