An array substrate, a manufacturing method thereof and a display device are disclosed. Patterns comprising a gate, a gate insulating layer and a polysilicon active layer are formed on a base substrate by single patterning process. A passivation layer is formed on the substrate surface formed with the patterns, and patterns of a first via and a second via are formed on a surface of the passivation layer by single patterning process. Patterns of a source, a drain and a pixel electrode are formed on the substrate surface formed with the patterns by single patterning process. The source is electrically connected with the polysilicon active layer through the first via, and the drain is electrically connected with the polysilicon active layer through the second via. A pattern of pixel defining layer is formed on the substrate surface formed with the patterns by single patterning process.