The invention relates to a heat exchanger dirt characteristic monitoring method. The method is characterized by comprising manual hard water preparation, bath temperature setting, performing of a dirt experiment, data measurement, calculation of heat absorption capacity of working medium component, replacement of an experiment tube, change of flow speed of experimental media and the like. The experiment tube made of stainless steel is assembled in an experiment system; a variable frequency pump is started, working media are sent to an experiment tube section for heat exchange, and heat absorption is performed; on-line measured parameters of the temperature, the flow speed and the like of the working media, the parameters of the experiment tube and the like are substituted into a working medium component unit time heat absorption equation, and the change tendency of experiment tube dirt characteristics changing with time is reflected by drawing a heat absorption curve of working medium components. During use, the on-line monitoring system is started, and signals of an inlet temperature, an outlet temperature, the flow speed and the like of the experiment tube are acquired and input into a computer for calculation of the heat absorption capacity of the working medium components. The heat exchanger dirt characteristic monitoring method has the characteristics of scientific, reasonable and feasible properties, high practical application value and capability of rapidly and accurately monitoring the heat exchanger dirt characteristics.