Abstract: With MATLAB software, the fouling of high-pressure heat exchanger in a gas oil hydrogenation unit was calculated throughout 3-year operation. The calculation results showed that the fouling rate of heat exchanger during operation was controllable; at the final stage of operation, the total resistance of scale was 1.2×10-3 (m2?K)/W. Based on the calculation results of fouling rate, the injection of scale inhibitor during operation was gradually reduced from 100 μg/g to 25—35μg/g, so that in this single operation cycle, the cost saving of scale inhibitor reached 11.59 MRMB. Besides, a fouling calculation method of heat exchanger based on ASPEN PLUS software and film coefficient theory was set up and the accuracy of this method was discussed as well.