With the development of power system load and grid structure, the transmission congestion caused by the uneven distribution of power flow becomes more and more serious, which greatly restricts the transmission capacity and efficiency of power system. Compared with the traditional scheme, FACTS has many advantages, such as small space, high controllability, etc. As the advanced third generation FACTS, UPFC and IPFC have advantages in power flow regulation. Therefore, it is necessary to study the technology and economy of the two in improving the transmission capacity of the system, so as to guide the selection of practical engineering solutions. First, based on the additional power injection method, the models of UPFC and IPFC are established. Then, taking the northwest power grid of Nantong as an example, calculations show that both can greatly improve the transmission capacity and safety reliability of the system. Finally, technical and economic solutions are explored under various working conditions. IPFC plays a more comprehensive and prominent role than UPFC in power flow regulation. This work is supported by Science and Technology Project of State Grid Corporation of China (No. SGJSJX00YJJS 1800739) and National Natural Science Foundation of China (No. 51407028).