I found a article about this: https://graspingtech.com/claim-bitcoin-cash-bitcoin-core-wallet/
1 Open Bitcoin Core.
2 Click on Help, Debug window and then click the Console tab.
3 If your wallet is encrypted run the following command: walletpassphrase [PASSWORD] 900 replace [PASSWORD] with your wallet passphrase.
4 Enter listaddressgroupings to list all public addresses.
5 For each public address run the following command to view the corresponding private key. dumpprivkey [ADDRESS] replace [ADDRESS] with one of the addresses in the output of the command in the previous step.
6 Copy each private key to a text file for later use in Electron Cash.[/li][/list]

I followed the first 4 steps and found that there are more than 100 addresses.
That will be too much work to do if I do step 5 and step 6.
Is there are easier way to do this?