Abstract: In view of the ultra-low emission of smoke and dust in China, the relatively single detection method of particulate matter and the urgent need for the training of electromechanical talents, a set of on-line monitoring instrument for ultra-low concentration particulate matter in diluted flue gas based on β-ray method was design. Firstly, the theory of measuring the concentration of particulate matter in flue gas by β-ray method is analyzed, and then the overall scheme of online monitoring scientific and educational instrument is designed, including the design of flue gas sampling system, measurement system and field control system. Finally, the test experiment of scientific and educational instrument is carried out under simulated smoke and dust conditions, and the concentration of particulate matter measured by β-ray method is compared with that measured by filter membrane weighing method. The accuracy of the online monitoring instrument is verified.