Abstract: Because that the substrates are always not planed. And the librations and rotations of the coating machines, the films are always uneven. It is very necessary to do more researches on the films' ununiformity. This article gave a briefintroduction to the coating process and the classifications. We explain the factors that influence the thickness and uniformity of the films and the coating speed that include the flow of the film, boundary layers, dynamic wetting line, dynamic contact angle and line. At the end of the article, we present the prospects of coating.