how far away if i go from beijing to great wall of china? how i can go to there?

Dessy, it depends on which section you are going to visit. The nearest part should be Badaling, about 70km from the downtown area of Beijing. You can take subway line 2 and get off at Jishuitan Station. Then get out from Exit A and walk to Deshengmen. There you can take bus no. 877 to visit the wall. It takes around 1 hour and 10 minutes on the way.