In message 200505111615.AA27132010@RCS-9000.COM you wrote:

Thank you for your answer! But how can I do next if I don't have ethernet to give kernel the rootfs and want linux run on my target board?

Use a filesystem on some other device, like a ramdisk image, or a cramfs or JFFS2 image in flash, or mount a file system on a harddisk or compact flash card or on a USB memory stick or ... there are many, many options. I don't know which options are available on your hardware, though.

This has nothing to do with U-Boot.

Best regards,

Wolfgang Denk