An ultraviolet (UV) inkjet printing method providing a stacked printing edge with a smooth effect is disclosed. After an inkjet head is controlled to print an image X on a substrate, a distance between the inkjet head and a surface of the substrate is kept unchanged, and the inkjet head is again controlled to print bi-directionally for at least once on the image X. After completing the above steps, the inkjet head is further controlled to print an image X′ on the image X on the substrate, wherein the image X′ consists of pixels expanded from the image X, such that the image X′ completely covers the image X, forming a smooth arc surface at peripheral edges of the image X.