A model for transmission lines maintenance scheduling is presented. The mathematical model takes the combination of all lines' maintenance startup time as the decision variable， and the minimal increased lack of load risk due to the transmission maintenance within the whole layout period is treated as the target in searching for the best maintenance scheduling. Meanwhile all lines' maintenance startup time is limited to the range of its maintenance startup-time-choice during the search. An algorithm from Tabu search is presented with the feasibility of the model and the algorithm is validated by simulation calculation.