20 hour layover at Beijing airport. Can I get some transit visa or permit to go out from airport?

Well, you don't need to have the visa because your stopover is within 24 hours. But if you wanna go out of the airport, you need to apply for the stay permit.

Before landing, you need to complete the "embarkation/disembarkation card". Then present it together with your travel documents, boarding pass for the onward connecting flight and travel itinerary. Go to the inspection counter of China Immigration Inspection to apply for 24h stay permit.

Thank you Duncan for your help.

Where I can find that "embarktion card"?

The staff on the plane will give it to you before landing at the airport.

Thank you again!