Measurement and monitoring of fermentation parameter is a very important way for obtaining the information of fermentation process, and also is the basis of optimal control. But, until now, most bioinformation is obtained offline, and the bio-information can not be used for control system on-line. In this paper, an on-line measurement system is developed based on the image processing technique. The developed system includes circulation and control part of solution, optical measurement part of solution, image catch and process part, computer and the software programme. The developed measurement system is compared with an existing spectrometer. The experiment results proved the proposed method and system can be used in on-line measurement system for development of other analytical instruments.