The cross-correlation flow measurement technique is a promising method in the two phase flow measurement field. Further research is conducting to utilize this technique in the measurement in paper industry. Emphasis is placed on the design of the polarity correlator for flow measurement, the accuracy of metering and the analysis of correlator characteristics. The paper presents a state-sequenced polarity structure of the simple digital correlator with variable length pre-delay based on a sophisticated microprocessor. The dynamic data tracking feature automatically adjusts clock of the hardware and time constant to compensate for rapid fluctuations in flow rate. The variable length pre-delay expands the flow velocity range to be measured and saves the calculation time. Finally the paper also presents the test that the ultrasonic flowmeter including an ultrasonic flowmeter including an ultrasonic double sensor and the correlator operated in a 33.7 mm diameter tube in which pulp suspension was flowing. The experiment indicates that the cross-correlation velocity is linearly proportional to the reference flow velocity measured by magnetic flowmeter. All the designed automatic features operated satisfactorily.