Modal damping is a kind of system damping in which the rotating machinery reaches every order modal shape. It is an important parameter in the dynamic response of rotating machinery. Due to the drawbacks of the traditional half power method, this paper proposes anew modal damping measurement method—the phase matching method. The phase matching method is to obtain the minimum distance estimation for the test phase data varied with the speed in order to determine the damping coefficient. This method is measured on rotating test equipment, and the obtained modal damping coefficient is close to the value obtained from the half power method. Theory analysis and test results show that when compared to the half power method, the phase matching method has the advantages of high safety and good stability.