If I have a bitcoin-core hd wallet in which there are 10 user accounts.then a user with its own private keys can access some other account data or not?
Please help me! thanks
You should explain better what you have there.
A wallet contains one or more addresses. Usually it also contains the private keys for those addresses too (you can safely assume that your wallet contains the keys too).
This means that everybody working on that machine and can open the wallet software will have full access to the funds.
You can password protect the access and/or the spending of the funds, but, as others said, someone else can install a keylogger and get your passwords and steal your money.
Keep in mind that whatever wallet you use (unless you use a hardware wallet), your money is as safe as your computer is.