Is there a fitness center or gym in Guiyang? I will be coming there to teach, and I need gym.

You can go to "Yaomei Fitness Club". It has many kinds of fitness facilities and good service. It is located at 2nd floor, no.47, Chengji Road, Yunyan District.
There is the another one that I would like to recommend to you. "Feirui Fitness Club" is located at 5 floor, Xingtiandi Building, West Zhongshan Rd., Nanming District.

Hope you like. :)