HI ,i would like to volunteer to take care of the pandas for a day while I'm visting chengdu how

It is hard to tell you whether you can do this or not. Anyway, you can go to visit Chengdu Panda Breeding and Research Center when travel to Chengdu and ask about this from the staff.

Hi there,
What the exact time do you come to Chengdu? And how many days you plan to be a volunteer at Panda Base during your stay in Chengdu? What kind of jobs do you want to do? Prepare the food for pandas; clean the excrement, or to be a scientific guide at Nursery Facility? It must be noted that to be a volunteer at Panda Base is really a hard work. You must work as common panda keeper and do a lot of work every day.