how to go from yonfu road to canton fair by metro?

There is no direct subway that can take you to the destination. You need to transfer.

Walk to Huanghuagang Station, and get off at Quzhuang Station. Then take subway line 5 to Zhujiang New Town and transfer to subway line 3 to Kecun Station.
After that, take subway line 8 to Xingang East Station, Exit A. It takes around 35 mins. The ticket fare is CNY 4 per adult.

Walk east along East Xingang Road around 450 yards and you will get to the exhibition hall.