The present invention discloses an active layer and a method for preparing the same, an organic field-effect transistor and an array substrate. In the method for preparing an active layer according to the invention, the active layer is pentacene layer, wherein the pentacene layer is prepared by a compound of the following Formula I as a precursor of pentacene. The active layer of the invention is prepared by the preparation method of the invention; the organic field-effect transistor of the invention includes the active layer of the invention; and the array substrate of the invention includes the organic field-effect transistor according to the invention.