i am at chengdu tianfu square, which bus goes to the global center?

You can walk to South Renmin Road 1st Section bus stop to take bus no. 118 and get off at Tianfu Avenue Shijicheng Lukou North. Then your destination is around 980yd away.

But local metro is more convenient. At Tianfu Square station, you can take metro line 1 and get off at Jincheng Square. Leave through exit A and you can spot the global center.