I have a Schengen visa valid from October 1st to October 30th 2014. First country of visit is Belgium and after I want to go for Germany. It is possible to go back to Belgium after Germany?
It's not a problem. As long as you don't exceed your visa's maximum stay or period of validity, you can stay in the Schengen area and crossing internal borders (borders between Schengen countries) does not make any difference. In all likelihood, you won't even see a border guard when traveling between Belgium and Germany.
Your visa will also have a specific number of allowed entries (1, 2 or ‘MULT’ for “multiple entries”, which means no limit) but that's only relevant when crossing external borders (borders between a Schengen country and some other country that is not part of the Schengen area).