(Solved) using SSH download image,but the disk is full

I follow this guide.
https://www.linode.com/docs/platform/disk-images/copying-a-disk-image-over-ssh/

But it shows:

Dd: writing to'/ linode.img': No space left on device.
1510649 ≤ 0 records in.
1510648 ≤ 0 records out.
773451776 bytes (773 MB) copied, 61.5391 s, 12.6 MB/s).

I use df to see things like this:

Filesystem 1K-blocks Used Available Use% Mounted on
tmpfs 756384 756384 0 100% /media/ramdisk
/dev/sdh 163036 163036 0 100% /media/sdh
/dev/loop0 149504 149504 0 100% /media/compressed_root
unionfs 756384 756384 0 100% /
devtmpfs 10240 0 10240 0% /dev

It seems like using ramdisk, which is obviously not enough to my img.
what should i do?

I'm stupid.

I use putty ssh to control server download img to itself..
I should run ssh locally