A method capable of reducing a required capacity of a retry buffer of a link device when the link device transfers real-time data to a link partner through the PCIe interface determines how to resend a packet required by the link partner according to the type of the packet. When the packet is a data packet, the method determines if a pending data packet exists in a pending transmission data buffer. When the pending data packet exists in the pending transmission data buffer, the link device directly transmits the pending data packet to the link partner. When the pending data packet does not exist in the pending transmission data buffer, the link device transmits a dummy packet to the link partner. In this way, the retry buffer only requires enough capacity to store the dummy packet and buffer the command data packets.