Abstract. Based on analysis on multiple packet losses of standard slow start caused by exponential growth of congestion window (cwnd), this paper proposes a new phase-divided TCP start scheme and designs a parameterized model to reduce packet losses and improve TCP performance. This scheme employs different of cwnd growth rules while cwnd is under and over the value of half window threshold (ssthresh) respectively, namely exponential growth and negatively exponential growth, which greatly decreases probability of multiple packet losses from a window of data and guarantees that a connection smoothly joins the Internet and transforms into congestion avoidance. Parameterized model adjusts the duration of slow start and acceleration of increasing cwnd to improve performance of slow start phase through various parameter setting. An adaptive paraeter setting method is designed. And the simulation results show that this new method significantly decreaseds packet losses and improves the stability of TCP and performance of slow start, and also achieves good fairness and friendliness to other TCP connections.