Hello Mei,
I won't lie. I think one day at Disney World is better than none. So if all you can swing for your first Disney vacation is three days, I say go for it!
I have traveled to Florida and visited the World in three short days before. I think you will be able to squeeze in a lot each day at the Parks. And, if you go into your trip knowing you may not get to ride all of the attractions or see every show, you'll be in good shape. If you can, try to invest in a good plan, like those over at TouringPlans.com, so you're armed with a strategy to really maximize your time.
And don't forget, if you are staying at a Disney Resort, be sure to take advantage of the
Extra Magic Hours each day. That way you'll get more time to play inside the Parks!
Hope this helps! Enjoy your trip!