Both in T3?! As I know, you do not need to claim baggage, custom, exit and re-enter the airport. China airlines assure the transfer between international flights can be finished in one hour. Of course, this is the fastest. Two hours are enough for you. After getting off the plane and get into the terminal building, go to the transfer counter, showing your connecting flight ticket and then go to the boarding in the second floor. If you do not have connecting ticket, it will be a bit complicated. You should claim baggage and pass the immigration and custom then get to the boarding area for next flight.
FYI: Transfer in T3 of Beijing Capital Airport(https://www.travelchinaguide.com/cityguides/beijing/capital-airport-transfer.htm) .