In network sniffing attacks, attackers capture and analyze network communication data from network nodes or links, monitor network status and steal sensitive data such as usernames and passwords. In an ongoing attack, the attacker is usually in a silent state, traditional network protection methods such as firewalls, Intrusion Detection System (IDS), or Intrusion Prevention System (IPS) are difficult to detect and defend against it. A Dynamic Path Hopping (DPH) mechanism based on Software Defined Network (SDN) was proposed to solve this problem. In DPH, the paths of communication nodes were dynamically changed according to constraints of space and time, and the communication traffic was evenly distributed in multiple transmission paths, which increased the difficulty of obtaining complete data in the network sniffing attack. The experimental and performance simulation results show that under a certain network scale, DPH can effectively defend sniffer attacks without significantly reducing network transmission performance.