Is the bus route from chengdu to jiuzhaigou is badly damaged by the earthquake ?

The bus route is not badly damaged by the earthquake. As far as I know, the earthquake does not effect the bus route seriously, so please do not worry about it.
For the bus near the bus station, do you mean the JZG Bus Station?
There are two buses stations in that place, one is in JZG county, about 14km from the entrance to the park and the other is in Jiutong Hotel, 10 minutes walking distance to the entrance.
The bus from Chengdu can reach the Jiutong Hotel, so you can live there.

If you use hostelworld i would suggest angelie hotel. Its only a 400m walk to the park entrance. Now in july 13 there is not direct service between chengdu and jzg a landslide caused the road to narrow so that only cars could get thru