Abstract: TCP incast congestion happens in data center networks with high-bandwidth and low-latency, when multiple synchronized servers send data to a single receiver in parallel. The existing improved methods focus on the congestion control algorithm in the congestion avoidance phase, ignoring the aggressive exponential increasing window in the slow start phase that is a key reason for incast problem. Therefore, this paper proposes an ECN-based slow-start of transmission control protocol (TCP) congestion control strategy, which dynamically feedbacks congestion status by using the existing congestion flags to adjust the window-increasing speed during the slow start phase. Experimental results show that our approach helps the existing data center TCP effectively avoid the throughput collapse in concurrent transmissions. The number of concurrent flow and network throughput are increased by 3.4×and 85×, respectively.