my existing disk details

lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
nvme0n1 259:0 0 477G 0 disk
├─nvme0n1p1 259:1 0 64G 0 part
│ └─md0 9:0 0 64G 0 raid1 [SWAP]
├─nvme0n1p2 259:2 0 4G 0 part
│ └─md1 9:1 0 4G 0 raid1 /boot
├─nvme0n1p3 259:3 0 200G 0 part
│ └─md2 9:2 0 199.9G 0 raid1 /
├─nvme0n1p4 259:4 0 1K 0 part
└─nvme0n1p5 259:5 0 209G 0 part
└─md3 9:3 0 208.8G 0 raid1 /home
nvme1n1 259:6 0 477G 0 disk
├─nvme1n1p1 259:7 0 64G 0 part
│ └─md0 9:0 0 64G 0 raid1 [SWAP]
├─nvme1n1p2 259:8 0 4G 0 part
│ └─md1 9:1 0 4G 0 raid1 /boot
├─nvme1n1p3 259:9 0 200G 0 part
│ └─md2 9:2 0 199.9G 0 raid1 /
├─nvme1n1p4 259:10 0 1K 0 part
└─nvme1n1p5 259:11 0 209G 0 part
└─md3 9:3 0 208.8G 0 raid1 /home

df -h
Filesystem Size Used Avail Use% Mounted on
devtmpfs 32G 0 32G 0% /dev
tmpfs 32G 0 32G 0% /dev/shm
tmpfs 32G 588K 32G 1% /run
tmpfs 32G 0 32G 0% /sys/fs/cgroup
/dev/md2 196G 1.7G 184G 1% /
/dev/md1 3.9G 441M 3.3G 12% /boot
/dev/md3 205G 28K 195G 1% /home
tmpfs 6.3G 0 6.3G 0% /run/user/0

now my requirement is i need to create a folder like /backup and assign some space from /home. bcoz only /home have enough space

So, you have a requirement - what have you done to investigate a viable solution ?. We can comment on your solution(s).

Edit your post and add [code] ... [/code] tags around those output listings to retain layout for readability.

You may find this article a good starting point.

Before you go trying anything, be sure to back up all crucial data to external media, just in case something goes wrong.

Speaking for external media, an alternative might be to get an external USB drive of adequate size and back up to it.

Both / and /home are only 1% used.

I assume that you are asking about creating a separate RAID 1 partition for /backup? Are you still running CentOS and if so what version?

CentOS by default uses xfs filesystem which can not be reduced. The only way would be to copy everything, resize md3 and then create a new filesystem. Since your home only shows 28K used I assume this is a new install and basically /home is empty?