Aiming at the disadvantage of the instrument for measuring the regulating characteristics and sensitivity with mechanical potentiometers，a digital design is used to improve its performance. Based on the original instrument，mechanical potentiometers are replaced by digitally controlled potentiometers. The wiper terminal of the digital potentiometer is controlled and displayed by single-chip microcomputer with a keyboard and a digital tube. The digitally controlled potentiometer can effectively reduce the reading errors of the movable terminal of the mechanical potentiometer. The improved device can not only accurately control and display the wiper terminal of digital potentiometer，but also be easy to operate. The curves of the regulating characteristic and the regulating sensitivity are measured，which show a good coincidence of the theoretic results.