The vibration tests of the double crank ring-plate-type cycloid reducer driven by three gears are tested and analyzed with the HEAD acoustics multi-channel vibration test and analysis system. The tests of the reducer are completed under the condition of different rotational speeds and different loads. The vibration distribution rules of the reducer are obtained. The three dimensional model of the ring-plates of the double crank four ring-plate-type cycloid reducer with Pro/E are established, the modality analysis are carried out on the model by the use of ANSYS. The natural frequencies and the corresponding vibration models of the ring-plates are gained. The results are well consistent with that of the vibration tests which provide the basis for further study of vibration and noise reduction.