A screening method of a phosphor-based optical film used in a backlight module and a backlight module are proposed. The screening method includes steps of: a) dividing an internal surface of the backlight module without a phosphor-based optical film into multiple measurement zones, and gaining a transmittance spectrum of each of the measurement zones; b) gaining a chromatic value of each of the measurement zones matching the phosphor-based optical film; c) checking the chromatic values gained in b) to be within a range of standard chroma; the process of screening being finished if all of the chromatic values are in the range; matching at least one measurement zone with a new phosphor-based optical film if the chromatic value of the at least one of the measurement zones is not within the range, and returning to b). The present backlight module has higher saturation and penetration and better color uniformity.