The uncertainty in generation and load growth as well as generation capacity variation has set new requirements on power transmission expansion planning adaptability and flexibility. The generation capacity adaptability index is introduced to improve network power transfer capability and enhance its operation ability to withstand generation capacity variations. A new multi-objective power transmission expansion planning model is developed to optimize multi-scenario network expected load factor distribution and generation output capacity adaptability. Its objective is to improve the system operation environment and network power transfer capability， minimize system load shedding in all research scenes and enhance planning network operation adaptability and flexibility. The effectiveness of the model and methodology proposed is shown by the results of two typical systems.