I will arrive at 23:50 at the capital airport (PEK), how can i go to "Capital medical Univesity"

You can take shuttle bus Xidan Night Line to Xidan and the bus operates till 02:00 the next day. Then the university is about 7km away. You can take a taxi to get there. If taking a taxi directly, you need to spend CNY120-130.

To get back to the airport, you can walk from your campus to Caihuyingqiao East bus stop and take bus no. 83 to Xuanwumen. Then take subway line 2 to Dongzhimen. Then get on Airport Express to PEK.