In my old computer some addresses have bitcoin and it is showing on blockchain.
When i am trying to get balance of the same addresses in my new computer where i have synced bitcoin full node ,I surprised addresses showing zero balance.
I am very confused, how can i backup bitcoin wallet from old computer to another
This method is used by Bitcoin Core (and few others) and comprises of backing up a wallet.dat file. It's a file that holds keys to spend outputs, addresses, transaction information, and other metadata such as contacts.
It has a different location based on an operating system.
Windows: %APPDATA%\Bitcoin
Linux: ~/.bitcoin/Mac OS X: ~/Library/Application Support/Bitcoin/
For backup Locate wallet.dat and copy it to another device only you have an access to. It may be a USB drive, CD, another computer or your private home cloud storage.
You may also copy it to a cloud storage such as Mega or Dropbox but make sure it's encrypted.
To restore the backup, simply copy your backed up wallet.dat over an existing one in the bitcoin data location.
You need to copy your wallet.dat from your old computer to your new computer and replace the file. Otherwise you could take a look on Electrum, it is a light wallet (so you do not need to sync the whole blockchain) and you can import your wallet.dat also there. In your wallet.dat all adresses and private keys are stored so you only need to backup this file.
