Finally, thanks to a lot of help from Derrick Sobodash, a user of the Beijing GNU/Linux user group I managed to install Debian into the Lemote Yeeloong.
Read it here
0. Download the debian loongson image: http://bjlx.org.cn/loongson/loongson2_debian5_20090108.tar.bz2
1. Use gparted to format a partition on a USB disk to ext3.
2. Mount it, change to the folder inside the usb /, and run `tar xjpvf /yourpath/loongson2_debian5_20090108.tar.bz2
3. Open /media/YOUR_NEW_EXT3/etc/fstab and comment out all lines except proc.