Getting a train is the easiest, fastest and cheapest way of getting to Badaling. Go to Beijing North Station just by Xizhimen subway station and from there buy a ticket at the 售票厅 (ticket counter). Tickets only cost 6 rmb one way and trains leave every half hour or so throughout the day. You don't have to buy the tickets days in advance either as there are so many trains that depart per day. You should be able to get a ticket there and then. Journey time takes about 1 hour approx. Do be prepared for a stampede of people when getting on and off the train though.

Get a bus its cheaper than a train and a nice ride and they pick you up right there, and of course you get a seat  check on line