We measured rocking curves of reflection high-energy electron diffraction (RHEED) from ZnO(0001) polar surfaces. It was found that the rocking curves for each Zn- and O-terminated surface differ considerably. The relaxed structure of each polar surface was obtained from first-principles calculations using density functional theory. The results reveal compression relaxation of the top bilayer. Experimental rocking curves of each polar surface have been successfully reproduced by dynamical calculation of RHEED based on their relaxed surface structures. It was demonstrated that the RHEED method can identify the polarity of ZnO(0001) surfaces.