In recent years, economical and environmental reasons have forced the transmission systems to be operated closer to their security limits. Power utilities world-wide have become even more concerned with various power system stability problems. In this paper, we mainly concern power flow control strategy on some system critical interfaces. A control method based on power flow tracing and generator re-dispatching is presented. It can effectively control the power flow on some critical interfaces in a relatively large range. Power flow on the interface is first traced backward to locate generators to be adjusted in the sending-end subsystem. And then, it is traced forward to determine loads to be affected. Power flow tracing is adopted again from such loads to determine their supplying generators in the receiving-end subsystem, which is then used to compensate the load fluctuation on the interface. Since power flow tracing is mainly used in the congestion management, power loss allocation, node pricing in deregulation study, the presented method can not only be used in the traditional and monopolistic environment to enhance power system stability, but also can be used to mitigate power system congestion under deregulation environment. Finally, New England 39-bus system, 57-bus system and 118 bus system are employed to verify the effectiveness of the presented method.