Developing of an effective flow control algorithm to avoid congestion is a hot topic in computer network society. This document gives a mathematical model for general network at the beginning, and then discrete control theory is proposed as a key tool to design a new flow control algorithm to avoid congestion in the high-speed computer network, the proposed algorithm ensures stability of network system. The results of the simulation show that the proposed method can adjust the sending speed and the queue level in the buffer quickly and effectively. In addition, the method is easy to implement and apply to high-speed computer network.