OK, I figure out the problem.
The rootfs.ext4 inside BSP is nothing.
I made a rootfs and put into the 2nd partition of SD card,
Just can't use dd command (I don't know why it occurs kernel panic),
sudo mount -t ext4 /dev/sdb2 /mnt/
sudo cp -a rootfs/* /mnt/
sudo umount /mnt
Modify env.cfg with
mmc_root=/dev/mmcblk0p2 rootwait
It boot into my rootfs successfully.
[ 4.427606] EXT4-fs (mmcblk0p2): mounted filesystem with ordered data mode. Opts: (null)
[ 4.436646] VFS: Mounted root (ext4 filesystem) on device 179:2.
[ 4.456482] devtmpfs: mounted
[ 4.460275] Freeing init memory: 352K
Loading, please wait...
Now, execute /init...
Welcome to ALLWINNER DEV
mount: mounting none on /proc failed: Device or resource busy
mount: mounting none on /sys failed: Device or resource busy
[ 4.720096] [DISP] disp_hdmi_set_detect,line:404:hdmi1's mgr is NULL
[ 4.730121] [DISP] disp_device_attached_and_enable,line:159:attched ok, mgr0<-->device1, type=4, mode=5
[ 5.057721] rtc_gettime(333): read time 1970-1-1 1:0:13
Please press Enter to activate this console.
[root@AW /]# ls
bin dev init linuxrc proc scripts tmp var
conf etc lib mnt sbin sys usr
[root@AW /]#