Optical density (OD) measurement, which is based on the selective absorption of light and the relationship between absorbance and material concentration, is a quantitative analysis method. As a traditional method of optical-electrical detection in modern biochemical analysis field, OD measurement has more advantages than fluorescence and chemical luminescence, such as wider application and easier implementation of photoelectrical detection, thus types of biochemical analyzers are developed with this function. In this paper principle of OD measurement is firstly introduced. Secondly, many types of biochemical analyzers utilizing OD measurement are discussed from the aspects of wave-bands and detection channels, because biochemical analyzer reveals diversity with the same principle of OD measurement, when wave-bands and detection channels change. Meanwhile, different wave-bands and detection channels enrich the application of OD measurement. Finally, this paper summarizes trend of the development of OD measurement technique.