An Escherichia coli analyzer based on substrate enzyme technology, with the analysis principle that Escherichia coli can produce an enzyme- β- D-galac cosidase. This enzyme can decompose ONPG and release ONP molecules, which dye the incubation medium yellow and can detect absorbance at a certain wavelength. It is soluble in water and has a hydrolysis degree of up to 15mg/L. When the yellow medium appears, it indicates the presence of Escherichia coli in the detected water. The degree of pollution in the water can be determined based on the duration of the appearance of the yellow substance. This method is applicable to the determination of surface water, industrial wastewater, and domestic sewage.