The first 512 bytes of MBR disk contains boot code and partition table, backing up (
dd command) this area is useful.
I have switched to GPT right now, and want make a backup, is it in the same way to MBR backup?
No, the first 512 bytes of a GPT disk are actually reserved for an MBR partition table called the Protective Partition Table. This table is optional, but the space is reserved for this. The next 512 bytes contain the GPT header, but that doesn't contain the partition table, which comes next. The partition table on a GPT disk is much larger than MBR table.
sgdisk program includes a way to make a backup of the GPT partition table, which you use like this:
sgdisk --backup <filename> <device>, where
<filename> is the name of the file where the backup is stored, and
<device> is the device name if the disk.