The traditional manual inspection of transmission lines has many deficiencies such as high labor intensity，high safety risks and low operating efficiency，which seriously restrict the intelligent transformation of the operation and maintenance for transmission lines． Unmanned aerial vehicle ( UAV) inspection has been continuously applied to the operation and maintenance of transmission lines for its high efficiency and high defect discovery rate． The application results of UAV in the transmission line inspection are studied，various constraints in the development of UAV inspection are analyzed，and the key technology to realize the intelligence of UAV inspection is discussed，which provides the research direction of promotion and development in UAV intelligent inspection．