How is the way from Dongsi Station to Mutianyu to see the great wall? Many thanks for your help.

Well, the route is a little complicated, but I’m trying to make it clear.
You can take metro line 5 at Dongsi and transfer to line 2 at Yonghegong Lama Temple Station, get off at Dongzhimen from Exit E.
Then walk east along Dongzhimen Outer Street for about 3 minutes and turn left at the first crossing, walk north for 5 minutes, you will get to Dongzhimen Public Transit Hub, from where you can take 916 Express to Huairou North Street.
After that, walk across the street to the same station to take Bus H23 and get off at Mutianyu Huandao. Walk northwest along Huaihuang Rd for about 10 minutes, you will see the ticket office of Mutianyu Great Wall.
It may take you more than 2 hours to get there.

thank you for your replay. Do you think Badaling is more easy to go? How do I get there? Thanks a lot for your help.

Yes, it’s much easier to get to Badaling, you are suggested to take a taxi to Deshengmen, which takes CNY20-30 and 10 minutes, form Deshengmen you can take bus 877 directly ro the Great Wall, and it takes CNY12 and about 1 hour.