Can I buy transport smart card and SIM card at Beijing Airport?

I presume you refer to Capital Airport. If so, you can get a smart card in the ticket center of Airport Express Train on B2 Floor, T2.

For SIM card, you can buy that of China Mobile near Gate no. 1, 1F, T2, and that of China Unicom at the Tourism Information Desk on 2F, T3. You should make it clear which card your phone accepts.

Hi Amelia,
What time does the airport express ticket counter open in the morning? thanks.

As I know, it’s available from 6:35 to 23:10 in T2; 6:20-22:50 in T3.