I would install Deepin on SSD in order to keep Windows on its' own disk away from the other distro. You could easily transfer W10 to the SSD and install Deepin on the HDD, but whatever you decide, I suggest you use different disks. I suggest this because W10 causes many boot problems. I have ,on my desktop pc, W10 on one SSD and Deepin OS on the other SSD, and so far so good. I first installed W10 on SSD and physically unplugged that SSD and then installed Deepin on the other SSD, and then reconnected the W10 disk, booted into Deepin and updated Deepin grub bootloader. This way, W10 can update properly without breaking anything. Whatever you decide, it's nice that you have two disks on a Laptop.

So I should unplug HDD when I`m installing Deepin on SSD, and one more question. How much storage does Deepin take ?

Whether or not to unplug W10 while installing Deepin is up to you. I suggested it because W10 will attempt to influence the behavior of both disks if you leave it connected when installing Deepin to the second disk. As for storage with Deepin, you probably need a minimum 15 to 30 GB, but you might need the full 120GB or more if your store a lot of videos, etc. on it. Hope this helps.

Thank you, it does help, in a couple weeks case caddy for SSD should arrive, and when I finish installation od Deepin I will let you know. Wish me luck

Good luck.

i installed win and Deepin in SSD while HHD used as such /home in deepin and D: E: in win .this gives me wonderful experience (very fsat) .
i first install win in SSD and install Deepin,and useto get win10 back.