Hami-Yongdeng transmission corridor connects the Northwest China power gird and Xinjiang power grid. It is proposed to allocate 750 kV controllable reactor on that line to improve the regulating and controlling capability to power flow and restrain the power-frequency overvoltage and secondary arc current. Base on the 750 kV transmission systems operating modes of Northwest China power gird in 2010 and 2020， the influences of high voltage controllable reactor on long term economic operation and dynamic performance of power system are analyzed. The economic benefit from the application of high voltage controllable reactor is also evaluated. Results show that its application helps to optimize power system steady state operation and improve its electro-mechanical and electro-magnetic performance. It is concluded that considering the economy， security and flexibility of power dispatch， it is preferable to allocate high voltage controllable reactor at Zhangye substation.