The invention provides a thin film transistor, a manufacturing method thereof, an array substrate and a display. The manufacturing method of the thin film transistor comprises the steps of: providing a substrate; forming an active layer on the substrate and a light shading layer covering the active layer through one-step picture composition process, wherein the light shading layer is formed by using a photoresist material; and forming a source-drain electrode layer and a passivation layer covering the source-drain electrode layers. According to the thin film transistor and the manufacturing method thereof, the light shading layer is manufactured on the active layer, so as to reduce a leak current generated by the active layer when the active layer is illuminated, and improve display quality; the light shading layer is made of the photoresist material, a photoresist layer is adopted as a mask during the preparation process of the active layer, and the reserved photoresist layer serves as the light shading layer covering the active layer after the active layer is manufactured; and the active layer and the light shading layer are manufactured through one-step picture composition process, an additional picture composition process is not needed, the technological process can be simplified, and the production efficiency can be improved.