The invention provides a power transmission network planning method and a power transmission network planning system considering new energy access. The method is provided based on an extended fuzzy opportunity constraint planning method. A power transmission network fuzzy robust planning method considering a new energy output interval model and a prediction load fuzzy model at the same time is provided. An equivalent power transmission network robust planning model considering a fuzzy load cut-set interval corresponding to a given confidence level is also provided. Finally, the power transmission network robust planning model is solved by adopting a particle swarm algorithm. An output global optimal scheme is taken as an optimal planning scheme of a power transmission network with new energy access. According to the method and the system, a power transmission network fuzzy robust planning method considering multiple uncertain factor interval models and fuzzy models is adopted, so thatthe adaptability to high-proportion new energy power transmission network planning is greatly enhanced. Compared with a power transmission network robust planning method only considering the new energy output interval model, the conservative property of the robust planning method is avoided.