Wallet.dat in the mobile hard disk is not backed up after sending Bitcoin Wallet.dat in the mobile hard disk is not backed up after sending Bitcoin, what can i do if the data recovery cannot found it? I have the original wallet.dat and private key， but there are no coins in it. help !!!
there are no coins in it.


Bitcoin wallets do not really contain coins. The only important information in a Bitcoin wallet is the private key (or several if you imported several rather than sweeping). Bitcoin wallets are more like your key-ring and not like the leather wallet in your back pocket.

Knowledge of how much money you control is in the public shared/replicated blockchain.

A wallet will typically show you a "balance" which is an amount it has calculated by examining the blockchain. A "full-node" wallet might not show the correct value for the balance if it has not yet "synchronised" its copy of the blockchain. An SPV wallet might show the wrong amount if it cannot contact a Bitcoin full-node. 


  Wallet.dat in the mobile hard disk is not backed up after sending Bitcoin


Although frequent backups are a good idea, you should be able to recover control over all your money just by using the private-key(s) (or seed-phrase for some wallets) to recreate your wallet. You should practice this sort of recovery. Neither the private key nor the seed-phrase change when you spend Bitcoin.