Now we can see some countries are regulating bitcoin and some government don't like it.Otherwise Bitcoin hasn't a stable price.
So my question is can bitcoin be a main currency of world economy?
It can still be used as a main currency of the world. However, I think it cannot be at the present state. It has to reach a certain level of stability, or else our world market will be in chaos more or less. We cannot entertain a currency which will be so volatile that what we can buy with a box of pizza today could only afford a piece of candy the following day. That cannot be a currency.