The invention provides an oxide thin film transistor, a manufacturing method of the oxide thin film transistor, an array substrate and a display device, and relates to the technical field of liquid crystal display. The manufacturing method of the oxide thin film transistor includes the steps that a grid electrode, a grid insulating layer and an oxide semiconductor thin film are sequentially formed in a substrate; first photoresist is formed in an active layer area of the oxide semiconductor thin film, and a channel area is thicker than a non-channel area; the first photoresist of the channel area is reserved; a source drain metal thin film is formed on active layer patterns, second photoresist on the source drain metal thin film is reserved, and the edge of the first photoresist of the channel area is covered with the source drain metal thin film; source electrode patterns and drain electrode patterns are obtained. According to the oxide thin film transistor, the manufacturing method of the oxide thin film transistor, the array substrate and the display device, when the initial source electrode patterns and the initial drain electrode patterns are formed, the photoresist is utilized to replace a protective layer to protect an active layer, the final source electrode patterns and the final drain electrode patterns are formed through a photoresist stripping technology, and therefore the length of a channel of the oxide thin film transistor is shortened.