when I load the vmlinux symbol , I check the memory and find that no disassembly code near th symbol . Why?

YinWei,

This is a common error if the ELF executables (either u-boot or vmlinuz) do not have debug symbols. Double-check steps 7 and 8 of the page you referenced above.
processors.wiki.ti.com/.../Sitara_Linux_Training:_uboot_linux_debug_with_ccsv5

That is the most common scenario, but since the procedure shown in the page was created by the Sitara group I will forward this thread to their forum as the experts there are more knowledgeable about the procedure to do this.

Hope this helps,
Rafael