Sorry Lichun. You have a problem known as "free surface" and "multi-phase". You have air (gas phase) being displaced by the liquid (liquid phase) and the Flow Simulation is not built to handle that case (at least not at this release 2011). I know the program ANSYS CFX can handle these phenomena. For now you could simulate mass "flowing" out of the cup by using the kinematics program (SolidWorks Motion) with some balls in the cup and 3D Contact. Initially, try putting one solid cube in the cup and set-up 3D Contact between it and the cup, and it and a table component. Then when you get that running, try it with two cubes (make a contact group), then three, and maybe four. Next try round spheres! I believe some folks have already done this in the SolidWorks Motion product.
you may want to take a look at Blender, an open source program.
It will take a while to learn how to use Blender, but then you can make your pouring water simulation.
These codes, based on the principles of fluid dynamics, are more concerned about the appearance of the fluid motion than the actual physics. Use these with caution for real problems.
That being said, what they can do is really cool! I personally tend to like particle flows more because they are more aesthetic, like what Thiago Costa is doing at http://www.lagoatechnologies.com/. I'm lucky to have this scuplture near where I live.