In early of December, how long time do i need to take taxi from jiuzhaigou park to the airport?

It takes a little longer than an hour from the valley scenic area to JZG Airport by taxi. And you'd better leave 1.5-2h to check in at the airport. Considering all, you'd better leave at least 4h in advance, around 12:00 at noon. Just for your reference!

If i fly from chengdu to JZG and arrive airport at 1.20pm. Do u still i still manage to visit the valley park what can i see?

To my experience, time is not enough to cover the whole park then. I suggest you travel from the airport to JZG Scenic Area. Then check in at a nearby hotel or hostel. After that, roam around to see the surrounding Tibetan villages. In the next morning, start to fully enjoy yourself in the valley/park.