The invention discloses a selective explicit congestion notification marking method (SECN for short) for a data center; the SECN implementation is divided into two parts: 1, a sending end writes estimated flow rate into the head of a data packet; 2, a switch judges the state of the flow speed rate and the like by reading the rate value of the head of the data packet, and the switch marks the flowwith high sending speed rate. The method, namely the SECN, in the invention is a first ECN marking method for distinguishing the flow state, and the method is low-load. According to the method, the link throughput can be obviously improved, the flow finishing time can be shortened, and the throughput of the multi-bottleneck flow can be improved.