Synchronizing torque and damping torque of a generator are two main factors influencing the stability of a power system， and they are organically combined with torque area. A novel method to calculate the torque area is proposed. In light of maximun torque area principle， the design of STATCOM stabilizer is optimized， and the problem of synchronizing torque being deteriorated by STATCOM is solved. When the stabilizer is put into place， it can maintain enough synchronizing torque and damping torque at the same time. This will significantly improve the stability of a system. The simulation results on EMTDC demonstrate the effectiveness of the proposed method.