Rotational speed monitoring is a critical part in the automatic control system of large generators and centrifugal machine. This article designed a rotational speed measurement system using electrostatic sensors and a correlation signal processing method. Two categories were utilized for the speed measurement-two sensors using cross-correlation method and a single sensor using auto-correlation method. Meanwhile, further signal processing methods were adopted to improve the accuracy of measurement results. Experimental tests were carried out on a laboratory-scale test rig under a rotational speed range from 400r/min to 3800r/min. The results show that the linearity of cross-correlation method and auto-correlation under experimental conditions is 1.53% and 0.52% correspondingly. In the same time, the auto-correlation method has a higher accuracy than cross-correlation method with the relative error lower than 1%.