Abstract: Variablestructure congestion control protocol (VCP) is an effective congestion control mechanism for high bandwidthdelay product networks, but the fairness of VCP asynchronous flows with large round trip time (RTT) variance become worse. To address this problem, the fairness of synchronous and asynchronous flows is analyzed based on the NS2 system respectively, and then a simple steady state throughput model is proposed. The state throughput of VCP flows is associated with the mean of multiplicative decrease factor of the VCP fairness algorithm. By adaptively adjusting the weight of addictive increase factor of the VCP fairness algorithm in end systems, the fairness of asynchronous flows is improved effectively. Finally, the improved algorithm is verified with the NS2 system.