How can i reach from fujiapu bus station to changsha airport?

I wonder if you refer to the Fujiapo Bus Station in Wuhan? If so, walk to the nearby Wuchang Railway Station to take a train to CS first within 3-4h. Near the rail station, you can take shuttle bus to the airport directly. This can be the best way. If with long-distance bus, only one schedule is available from Fujiapo Station, at 14:40.

Thank you Serena for your kind information... But while coming back (mid of February), I will reach huanghua airport 11.30pm. So I am confused how will get back to wuhan that night.

Well, according to your arrival, there is no direct public transportation that can take you to Wuhan. So you need to find a hotel nearby the hotel. In the next morning, take airport shuttle bus to get to South Railway Station. The transfer to high-speed train to get to Wuhan Railway Station.