Waiver for conference registration fee Usually there are some ACM/IEEE conferences which takes registration fee around 350 to 550 US dollar. For a student, it might not be possible to deposit such amount of money. 

Under this circumstance, is it ok to ask conference organizer for 100% waiver in registration fee?
The dominant cost of attending most conferences is not the conference fee but the travel costs (e.g., airfare + hotel). Moreover, most conferences (including most ACM and IEEE conferences) offer a reduced rate for student attendees, often half or less of the rate for professors. If you cannot afford that lesser rate for students, you probably cannot afford the travel costs either.

There are two good ways to try to get around these problems, however:


Some conferences offer the chance to apply for student travel scholarships. These typically both waive registration fees and help cover travel expenses.
Many conferences draw on student labor to help run logistics, e.g., manning the registration booth, acting as ushers. These students are typically compensated by free registration. They are usually drawn only from the hosting institution(s), however.


The best way, however, if you are a graduate student, is to see if your professor or your department can support you.