When I arrive at Guangzhou airport (Baiyun) , is there direct transportation to HongKong ? Bus or train ?
You can take an airport express shuttle bus to go to Guangzhou East Railway Station (Guangzhou Dong Zhan). There you can take a train that goes to Hung Hom in Hong Kong (Tsim Sha Tsui in Kowloon). There should be buses departing from the airport regularly. Buses go to different parts of Guangzhou. You can ask the bus ticketing staff at the airport which which buses go to Guangzhou Dong Zhan. Bus fare is about ¥20. Bus ride time is one hour and 15 minutes if traffic is all right. Hung Hom-bound trains depart every 50 minutes or so at Guangzhou Dong Zhan, from 7 am to 9 pm. Check MTR Hong Kong for their schedules. Train fare from Guangzhou Dong to Hung Hom is HK¥190 for an adult. Train is a convenient and comfortable to go between Guangzhou and Hong Kong.
You can also take a subway train (Line 3) at Guangzhou Baiyun Airport to go to Guangzhou East Railway Station. From Airport South Subway Station (Jichang Nan Zhan) to Guangzhou Dong Zhan it is roughly 30 and the ride takes a little over 50 minutes.
If you take a taxi at Baiyun Airport to go to Guangzhou East Raiway Station, fare should be around ¥100.
At various hotels in Guangzhou you can also catch buses that go to Hong Kong. China Travel Service Hong Kong operate some of these bus lines during hours 7 am - 8 pm. Some of their pick up hotels - Hotel Landmark Canton, Guangzhou White Swan Hotel, Guangzhou Hua Wei Da Hotel, and China Hotel. Check with CTS Hong Kong about their operations. Hong Kong-based Trans-Island China Link have similar services. Their picups are Garden Hotel, Rosedale Hotel Guangzhou, Guangzhou Hotel, Yitai, China Hotel, Dong Fang Hotel. Bus fare is about ¥100.
We're not aware of direct transport link between Baiyun Airport and Hong Kong. You can look into it to verify.