I've received an offer letter but I feel the salary is lower than I expected. I am currently in my notice period with my previous employer.
Can I renegotiate my salary without jeopardizing the job offer?
can i still discuss with HR for salary
Since you haven't signed the offer, then you can still discuss the details, and perhaps have them changed.
It's unfortunate that you have already negotiated to the point where you got an offer letter with a 7 day turnaround period. Better would be to have negotiated your desired salary first. But it's still possible to continue the negotiation up until the point where you sign the offer.
Don't wait. Contact HR and tell them that after thinking about it more, you believe the offer is too low. Be prepared to give reasons why you feel that way. And be prepared to explain why you didn't give those reasons earlier in the negotiations.
If I negotiate with HR can my dream job in lose ?
Yes of course. That's the way negotiations work. Until you sign the offer letter the company can withdraw it at any time, for any reason. (They can do so later as well, but that's a different discussion).
You need to negotiate carefully here. The company may have another candidate that is almost as good as you are, or they may not. The company may feel that you are not worth the effort of negotiating further, or they may be willing to play along up to a point.
There's no real way for you to know how far they are willing to go unless you push them past that point.
You have to decide how much of a dream job this is, how much you really need in salary, and how much you are willing to risk.