Me and another PhD student, we are first two authors in a paper. We had a disagreement with our supervisor about submitting our paper to conference. We both opposed the submission as we think it's too early to submit our result and the paper will most likely be rejected. Our supervisor said, academically he has the full authority to submit the paper even if we oppose. My question is does a supervisor have the right to submit a paper from the point of view of the university?
Your supervisor does not have the right to submit a paper with your name as a coauthor without your consent. By making such a submission he would be making a false representation that all coauthors have agreed to the submission, thus essentially committing a form of minor fraud or certainly dishonest and unethical behavior that is considered completely unacceptable in the academic world.
Note that you write "from the point of view of the university", so technically there is a chance that your university has unconventional standards in such matters and in their eyes your supervisor is correct. If that is the case (which I strongly doubt), I would suggest getting the heck out of that miserable institution and going to a real university.
Finally, while it is absolutely possible that you generally have better judgment than your supervisor (a possibility that does not occur to many graduate students even when perhaps it should), he does have more -- probably a lot more -- experience than you in matters of publications, so I agree with jakebeal that it is worth questioning whether your objection to the submission is a good idea, and maybe consulting other experienced academics from your field.
Ethically, a paper should only be published with the active consent of all the involved authors. Thus, from an ethical point of view, your supervisor should not submit without your consent. If your supervisor does so, that is a clear breach of scientific ethics and needs to be treated very seriously.
On the other hand, are you sure that you are right in withholding your consent? You say that you think that it is too early to submit your result to this conference. Are you sure that you have a better idea of the size of contribution expected by this conference than your advisor?
You don't say how far along you are in your program and how much you have published before. It is common for early-career researchers to overestimate the size of a result necessary for a good paper. In my graduate program, for example, Ph.D. students were expected to produce a Masters thesis first, and a common failure mode was for students to essentially try to do a Ph.D. worth of work already.
It is natural to want to be able to submit a paper that definitively solves the whole subject, but in some areas, particularly engineering fields, it is more common to have a sequence of conference papers that build up piece by piece, followed by a capstone journal paper that ties it all together into the complete and thorough package. Conference papers can thus be reports of a significant step toward a result, rather than the result entire. You supervisor may be seeing a step of that sort in the results that you have so far, and it would be good to ask and see why your supervisor thinks the work so far is significant enough to publish.
Take a close look at your situation, compare with other papers published in the conference (not the award winners, but random papers in random sessions), and ask yourself how the size of your increment compares with theirs. You may find that it's reasonable to submit after all (the criteria is not: "Am I certain to be accepted?" it is: "Will the reviewers be annoyed that I am wasting their time?"). Or you may gather evidence that will let you make a stronger case for why you think your paper is not ready, and be able to convince your supervisor.