In this study, a method of rotational degree of freedom(DOF) measurement by Doppler laser vibrometer is presented. First of all, the Doppler laser vibrometer is used to obtain the synchronous translational time domain response of two adjacent measuring points. So that, the rotational DOF time domain response can be obtained by finite-difference technique, and then the rotational and translational frequency response functions will be obtained. Finally, the vibration modes can be obtained by modal analysis technique which combine the translational and rotational DOF of test points. The proposed procedure which is based on Doppler laser vibrometry is verified through the rotational DOF measurement of the plate，and solves the problem of rotational DOF measurement and identification effectively in the study of modal analysis.