I got a rooted MT6575 android phone and after some work,arch runs good.
First I installed busybox and ssh/sftp server(this just for Ctrl-C not exiting the shell) from Google Play.
Then,I connected to the phone via SSH.Browsing mirror site,I got the link of some key packages such as GLIBC,filesystem,coreutils,pacman ,bash,bzip2,chroot,fakeroot,gcc-libs,libxml2,libarchive,xz,libssh2,etc., using 7-zip to check the dep (a file start with dot in xz file),wrote the url into a text file.
made three partition file,fs_root,fs_lib,fs_share,run mkfs built to fs on them,mount them into /mnt/a ,/mnt/a/usr/lib,/mnt/a/usr/share as loop device.This may in case of data losing.
chdir to /mnt/a
paste the links into ssh console ,let wget download the packages.
all download finished,I used `for` statement to extract all the archive in a quick way.I moved /var/cache to external sdcard,and made a link in /var.
after that,I symbol linked the usr and usr/bin dir in rootfs ,chrooted using following command:
PATH=/usr/bin LD_LIBRARY_PATH=/usr/lib /usr/bin/fakechroot /mnt/a/bin/chroot /mnt/a /bin/sh