After a world wide flood, you would expect to find millions and millions of dead things all over the world covered by layers of rock and mud, Ah, come to think of it, that's jsut what we find, millions and millions of dead things all over the earth covered by layers of mud and rocks.
That is, of course, a gross oversimplification. Such a flood would have distributed fossils more or less randomly. Dinosaurs would be mixed in with humans and such.
That's not what we see in the fossil record. We have a fossil record that supports a long-term evolutionary process lasting hundreds of millions of years.