Abstract: For the experiment of laser diffraction,the measurement method of filament diameter based on laser diffraction imaging is put forward. The practical system is combining optical principle,image sensors,image processing,error analysis and data processing.In the experiment,two dimensional imaging sensor is used to capture the diffraction intensity distribution which can improve the precision of measurement. The method proposed in the paper can be applied in industrial online real-time measurement. Also,the experiment can greatly improve the understanding of optical application in the field of industrial detection for students.