If I create new wallet.dat on one electrum client, it is will be different wallets?
I need it for get my BTH from old btc wallet or I can't get my BTH if I will be use one client..
If you want to claim your BTH from an old BTC wallet, you can just:
1. Send your Bitcoins to a new wallet with Electrum;
2. Download Electron Cash[1] and open your old wallet with it - that doesn't have BTC anymore, but still has BTH;
3. Now you have a wallet with BTC and your old one with BTH.
Any wallet created on Electrum or Electron Cash are valid on both chains. This means that you can receive BTC/BTH on the same wallet (not recommended) and be able to spend both coins by using its proper software.
Bitcoin = Electrum
Bitcoin Cash = Electron Cash
P.s: wallet.dat is only for Core. Electrum will create a normal file without any extension.
[1] http://www.electroncash.org/