The whole electric power system includes four aspects: generation, transmission, distribution and electricity users. Those four aspects all need maintenance to enhance system reliability and energy efficiency. Under deregulated electricity market, generating unit maintenance scheduling arrangements are very different with the traditional electric power system. In the tradition electric power industry, dispatch agencies unified formulate maintenance scheduling which is not suitable for the electric power market mechanism. Generation maintenance scheduling that is determined by the power companies themselves may pose a threat to the reliability of the system. And the main purpose of transmission line maintenance is to ensure electricity delivery and avoid wasting of energy. Under the electricity market, the transmission line maintenance scheduling needs to cooperate with generation maintenance scheduling and distribution equipment maintenance scheduling. On the basis of the previous research, this paper mainly studies the generation and transmission maintenance scheduling under electricity market, describes the impact of electricity market on transmission maintenance scheduling and focuses on the model of coordination optimization of generation transmission maintenance scheduling. Keywords-Electricity market; electric generation and transmission; maintenance scheduling; optimal model