Disclosed is a low and weakly-interlaced industrial polyester multifilament yarn, which has excellent flatness and flat uniformity, and in which the number of monofilament layers is properly controlled according to a fineness of the low and weakly-interlaced polyester multifilament yarn and monofilaments are interlaced, thereby reducing a surface brightness gradient of a coated fabrics, produced using the low and weakly-interlaced polyester multifilament yarn, when light is irradiated to the coated fabrics. Additionally, the present invention provides a method of producing the low and weakly-interlaced polyester multifilament yarn, in which air pressure of an air interlacing device, a yarn path, tension of the yarn, an helix angle of the yarn wound around a cheese, intervals between first guides, located before and after the air interlacing device, and second guides, located in the air interlacing device, and a position of a wave plate are properly controlled.