Abstract: Up to now, the water content in crude at an interface point has been measured with manual method and distilling method, 2 hours for sample collection and 4 hours for experiment carried out manually. The collected samples are of no representitiveness, the method of chemical experiment is artificially interfered. To solve the above problem, China Measurement Research Institute has developed an analyzing meter of SH-E model for water content in crude analysis. Therefore water content can be measured on line continuously, instant display is available, it takes 2 hours to get and print out the average value. Artificial interferences can be avoided. As a result, the measured content of water in oil is of representitiveness. RF water content analyzer is only made up of a sensor of RF water content measurement, and a signal analyser with the Z80 single board computer as the core. RF method for measuring water content is based on the theory of RF resistance. The resistance characteristics of the oil/water liquid being measured to the RF signals shows the quantity of the water in oil. This instrument is wide in measuring range, high in sensitivity, good in stability, simple for installation and convenient for application. It also has the function of automatic expansion of measuring distance, automatic selection of the superior accuracy according to the measuring range. Through a month on line measurement, the instrument measuring result, compared with manual experiment, is convincible; compared with distilling methed, instrument measuring can save time, labour and energy, etc.