1. vi /etc/default/grub
2. modify the value of GRUB_CMDLINE_LINUX parameter , Ex : GRUB_CMDLINE_LINUX="vga=0x317".
Before changing it, backup orginal value is recommended.
3. there are some values for reference .
| 640x480 800x600 1024x768 1280x1024
---- | --------------------------------------
256 | 0x301 0x303 0x305 0x307
32k | 0x310 0x313 0x316 0x319
64k | 0x311 0x314 0x317 0x31A
16M | 0x312 0x315 0x318 0x31B
4. $sudo update-grub
5. $sudo reboot
Good luck to you!
Reference: http://blog.csdn.net/weilanxing/article/details/7664324