A method and a device for detecting plastic foreign objects with low chromaticity difference in shredded tobacco through online pulse spectral imaging are provided. The method includes three steps: negative pressure thin-layer loading of shredded tobacco, pulse line-scanning identification of shredded tobacco, and positive pressure online elimination of foreign objects. Loose shredded tobacco is formed into a fixed and continuous thin layer on a surface of a conveying cylinder under the effect of a negative pressure adsorption force. The surface of the conveying cylinder is coded by areas. An LED linear array light source containing characteristic wavelengths of plastics with low chromaticity difference emits optical pulses, and a line-scanning camera is used to obtain characteristic signals of the plastic foreign objects with low chromaticity difference efficiently in real time.