I'll arrive PEK at 5:30 am how to get the morning speed train to Cangzhou.

The speed ride to Cangzhou should depart from Beijing South Station. From PEK, there is shuttle bus to South station, but the bus should be available since 8:30am. The subway starts at 6:30am from PEK. By subway, you need to take the Airport Express to Dongzhimen first and then change to Line 2 there to reach Xuanwumen and finally take line 4 to the South Station. It would be better to have at least 2 hours on the way since it would be morning rush at that time.