When do we get negative rating?

In march long challenge, I made one successfully submission and still my rating for that contest was -1116
how this could be possile.

Your rating decreased by a large value to make it negative because your performance was below expectation.

Initially a new user is given 1000 rating and in the first contest if he/she does not perform well compared to what is expected from a user having 1000 rating, then the rating will decrease, otherwise it will increase.

You can find some details about this rating system here, here and here.

Your rating is also dropped if you are caught using false practice. More about false practise