How can I get from the Jiuhuang Airport to Jiuzhaigou? And how much does it cost? By bus? By taxi?

Well, you are not suggested to take the direct airport shuttle bus according to your arrival time. The bus schedules are not fixed and they rely on the density of flights.
So you'd better to hire a private car directly in advance. The fare is about CNY 300 at night.

Thank you for your reply, Rose!