Mrs.dewi, if you want to transfer to the Airport Express, you need to buy the separate ticket of CNY25.00; if it is other subways like line 1, 5, 4 13 and so on, you do not need to buy extra ticket, just change to the line.

Hello Mrs.dewi：
You can change to any subway line with no transfer fee except the airport express train.

no ticket is needed to be bought when you transfer to another line as line 1, 13, 4, 5.

2 rmb and thats it.

it is advantageous to get a bus pass. which is like 20 rmb for the card and you can put plenty of rmb on it which will save you loads of time if you get to a busy station. you won't need to wait in line for tickets.