Hi everybody!

I am looking for a PhD program.
I wonder by myself about the ranking is a key to get PhD when I apply research program, right?
and which is the best ranking university in the world?

It's a good indication, but it's not the "be-all-and-end-all" when it comes to choosing your PhD. It may perhaps be useful to know what subject you're wanting to do, and which countries you're interested in. Remember, different universities specialise in different subjects, but that doesn't mean that a small, almost insignificant department in some institute that doesn't specialise in your subject/research wont have a great and exciting opportunity for a novel PhD topic, and vice-versa.