As mentioned, it’s best to stay in the town of Wulingyuan and not Zhangjiajie City when visiting Zhangjiajie National Forest Park.
I stayed at Zhangjiajie 1982 Chujian International Youth Hostel during my trip and would recommend it. While I normally avoid staying in shared dorm rooms, I make exceptions for national park areas. I was able to sleep pretty well each night and met a number of friendly Chinese and foreign tourists alike.
Other positives include the staff being quite helpful with setting guests up with a park pass and explaining the best routes to take. And most importantly, the hostel is an easy walk from the Wulingyuan Entrance of the park so you’ll have no issues getting there and back each day.
But some of the downsides include booking a room that was advertised as 4 people max, only to check-in and discover 8 beds! Fortunately, though, this didn’t turn out to be a big deal, as it wasn’t always full and the other guests were friendly. Another annoying issue was the lack of a washing machine in the building. They actually make you walk all the way to one of their sister establishments if you need to wash your clothes.
Note that this place also has private rooms if you’re alone or traveling as a couple. And there are of course many other accommodation options around Wulingyuan, a town that pretty much just exists for visitors to the park.
Booking.com
But what about staying inside the park itself? Apparently this used to be possible several years ago, but this was no longer the case at the time of my visit. (Rumor has it that authorities banned park accommodation after part of a trail collapsed.)
With that said, there do appear to be some hotels still secretly operating within the park, which I came across by accident during one of my hikes. Furthermore, there were a number of elderly ladies along the trails mentioning that they had places where I could sleep, but due to the language barrier, I couldn’t get much detail.
So while it may technically possible to stay in the park, I’m not sure how you could arrange this without speaking Chinese.