I have 1 backpack and would like to keep in lockers.

The luggage storage service is available in Badaling and Shanghai Train Station.
Supermarkets, shopping malls, and bus station in Chengyang Disctrict in Qingdao all provided luggage storage service.
I didn't find the specific information at Longqingxia. If the luggage storage is not available, you can deposit it in one of the hotels near the scenic area. No worry!

Longqingxia. Hotel.

Is it safe? even though I didn't stay in hotel, ok to keep in there?
Suzhou train station- How long can I keep the luggage? overnight?
Most of luggage service, can i keep backpack overnight? Is it safe?

You can deposit the luggage at Yidu Holiday Hotel at the entrance of the Longqingxia. No worry!
It is definitely allowed to store your luggage at the Suzhou Railway Station for overnight. Just well keep the receipt. It is needed when you reclaim the luggage and pay the fee.
Generally, left-luggage offices at the railway station and bus station can provide overnight deposit service.
For supermarkets and malls, it is advised you reclaim it the same day and it is totally free. Or, you may need to contact the staff to get it back and pay extra fare for storing it overnight.