Hi 姚 玮
I would suggest you change the default FTP server configuration to see whether it helps
FTPSRVCFG_TX_BUFFER_SIZE: Size of the socket transmit buffer in bytes. This option cannot be overridden in runtime. The default value is 1460 bytes.
FTPSRVCFG_SEND_TIMEOUT: timeout value for server sockets in milliseconds, and cannot be changed during runtime. The default value is 500ms.