Google is your friend: Be nice and visit him often. He can answer questions a lot more quickly than posting them here...
A very quick search gave over 90,000 hits:
call matlab dll from c# - Google Search[
^]
The top result:
MATLAB Central - Using matlab dll in c#[
^] gives you links, code, examples, the lot.
In future, please try to do at least basic research yourself, and not waste your time or ours.