The present disclosure provides an array substrate, its manufacturing method and a display device. The array substrate includes operating circuit interfaces, testing interfaces, and testing lines connecting the operating circuit interfaces and the testing interfaces. Each testing line includes at least one cut-off point, and conductive contacts extending to an upper surface of the array substrate are arranged at two sides of each cut-off point of the testing line. When testing an operating circuit, electrically connecting the conductive contacts at two sides of each cut-off point enables the testing line to be conductive.