How do I get from the Beijing South Railway station to the Beijing Airport (PEK)?

You can take the airport shuttle bus Line 10 from the traffic hub in north exit of Beijing South railway station. And it take about 2 and half hours. You can also try to take the Line 4 from Beijing South Railway Station to Xuanwumen. Then change to Line 2 and get off at Dongzhimen and then take the airport shutle. This may make the time shorter like 90min.