When dynamical balance machine is used to measure the imbalance of the workpiece with large eccentric mass, due to the large imbalance the vibration signal usually exceeds the linear range of both the dynamical balance machine and measurement system, which results in grave error. In order to improve the accuracy of imbalance measurement, a method is proposed, which utilizes a controllable electromagnet to generate controllable electromagnetic force for attenuating the unbalance vibration synchronously, so as to avoid the vibration signal exceeding the liner range. The basic operation principle of the method is discussed, the equivalent magnetic circuit model of the electromagnet is established, and the relationship between the coil current and dynamic electromagnetic force is analyzed with finite element modeling. The influence of some factors, such as air gap and temperature on electromagnetic force is analyzed. The control system and control strategy are also introduced. Dynamical balance test experiment was conducted, the test results indicate that the proposed measurement method can effectively improve the dynamical balance test accuracy of the workpiece with large eccentric mass.