This paper studies the problem of the real-time communication in the on-line monitoring system, which achieves the on-line monitoring of B / S mode through the ActiveX controls and network programming technology based on the TCP / IP protocol. This paper proposes an improved congestion control algorithm grounded on the one-way delay (CCAOD), using the value and the change trendency of the one-way delay to determine the degree of congestion detected at the receiving terminal. This article divides the congestion level into eight grades according to the value of the one-way delay, and changes sending rate under the linear function of the level and variation trendency of congestions dynamically to achieve congestion control. The simulation results shows that the CCAOD can avoid network congestion more efficiently and improve the real-time performance of the system in the OMNEST platform.