A method for changing a transmission path of packets transmitted from a first node to a second node in a software-defined network is provided. The method includes removing a flow entry corresponding to a first transmission path on a flow table of the first node after a plurality of first data packets intended to be transmitted to the second node are transmitted from the first node via relay nodes of the first transmission path. The method also includes transmitting a flush packet to the first node and setting the flush packet to be transmitted to the second node according to the first transmission path; and when the second node receives the flush packet and transmits a packet inquiry message corresponding to the flush packet to the controller, setting a flow entry corresponding to a second transmission path on a flow table of the second node.