the nearest part of Great Wall to Haidian and how to get there

Teresa, I think you should visit Badaling section. I don't know where you dwell exactly. There are two ways: bus or train. If you plan to take bus, please go to Deshengmen. There you can take no.877 bus to reach the wall. If you plan to use the train, you need to reach Beijing North Railway Station. There you can take S2 train to visit Badaling section.