I'm a Danish citizens living in Belgium. I'm going to Beijing the 27/10 to 30/10. Do I need a visa.

Vibeke, if you fly to a third country or region rather than the last one you fly from after staying in Beijing for less than 72 hours, you can enjoy the 72 hour free transit in Beijing. In this case, no entry permit is required.
Otherwise, you need to apply for a tourist L visa in advance. You cannot apply for it online. You can go to the CVASC in Brussel to apply for it by yourself, or entrust someone else to go there and apply for you. You need to provide your passport and copy of its data page, the application form, a passport-style photo, your residence permit in Belgium, and proof of accommodation and transportation arrangement.