how use boot_hybrid.img make iso

[cheng wensui]

pc is bios , no uefi
I want to use boot_hybrid.img  make boot_hybrid.iso
#####################
xorriso -as mkisofs -r -J -joliet-long -l \
-isohybrid-mbr /home/cws/my-iso/boot/grub/i386-pc/boot_hybrid.img \
-b boot/grub/gcd.img \
-c boot.cat \
-no-emul-boot \
-boot-load-size 4 \
-boot-info-table \
-o boot_hybrid.iso /home/xxx/my-iso
#sdb is usb
dd  if=~/boot_hybrid.iso of=/dev/sdb bs=2M && sync 
#####################
rerun to usb,only display “GRUB”，not load grub.cfg
reruun to cdrom is ok can load and display grub.cfg
What did i do wrong