Hello I come from Frankfurt LH 720 and land in Capital Airport. Then fly on to NanjingCA1847

It's international to domestic transfer in T3. The correct transfer procedures are the following:
Inspection & Quarantine, Exit and Entry Frontier Inspection - Baggage Claim - Customs Inspection - Going through Transfer Formalities - Security check - Waiting & Boarding
By the way, generally speaking, you need at least 2 hours to make this transfer. Hope helpful!