Hi, just wondering if we need to take cable car to Jiuzhaigou?

As I know, there is no cable car service in Jiuzhai Vellay Scenic area, so you do not need to worry about that.
There are sightseeing buses taking you to tour around all the spots, you can get on and off at any spots that you want to visit further. It is safe and comfortable.

Sarah, thank you very much for your reply.

I saw from you-tube, travellers from Jiuzhai Gou to Tian Men Shan and they took the cable car (without doors) and legs dangling out. It looks so scary.

Oh, you must misunderstand that. It is not in Jiiuzhai valley (Sichuan Province). Tianmenshan is one of the spots in Zhangjiajie scenic area (Hunan Province). They are not the same place and located in different provinces.