In solving the transmission line maintenance scheduling optimization problem(TMSOP) under electric marketing circumstances, a chance-constrained bi-level programming model and a hybrid intelligent algorithm are put forward. The model takes into account the uncertainty involved in TMSOP and the maintenance economy versus power system reliability, while evaluating the probability and consequences of insecurity. The Monte Carlo simulation based hybrid intelligent algorithm is proposed to solve this model, with the taboo list to improve the calculation speed. Finally, the IEEE RTS-79 case results demonstrate that the model and the algorithm can not only optimize the maintenance schedule with the most economical resources arrangement but also recommend the least-risk-operation modes for the power system during maintenance.