With the rapid growth of rate based services and wireless applications,improving Transmission Control Protocol ( TCP ) congestion control has been becoming more important in the network research field. This paper first briefly introduces the Additive Increase Multiplicative Decrease ( AIMD ) (a,b) algorithm,and then presents an improved TCP congestion control mechanism (D AIMD) whose principles and simulation results are discussed in detail. This mechanism can be easily implemented with lower additional overheads and can efficiently improve network performance. With the rapid growth of rate based services and wireless applications, improving Transmission Control Protocol (TCP) congestion control has been more important in the network research field. This paper first briefly introduces the Additive Increase Multiplicative Decrease (aIMD) (a, b) algorithm, and then presents an improved TCP congestion control mechanism (D AIMD) whose principles and simulation results are discussed in detail. This mechanism can be readily implemented with lower additional overheads and can advantageously improve network performance.