How to bring down the anger of a child?

Talk to them in a very soft voice. They can't hear what you are saying so they don't have much of a choice but to stop screaming so they can hear what you are saying. Then find out what is wrong and hopefully a big hug will be the cure. You haven't said what age the child is but this is my recommendation.

I myself do not have any kids but when I have baby sat a young child who starts to throw a fit. What has always worked for me is talk to them find out why there upset. or tell them that throwing a tantrum isn't going to get them any where it's just going to get them left sitting on the floor. That has always worked for me.