The invention relates to a testing method of vibration of a structure in a flow field, in particular to the testing method of vortex-induced vibration of a cylinder. In the method, a testing device which can independently control the two-degree-of-freedom vibration along the flow direction and the transverse direction respectively is utilized for performing two-degree-of-freedom vortex-induced vibration testing and single-degree-of-freedom vortex-induced vibration testing respectively, analyzing phenomena and data of the two-degree-of-freedom vortex-induced vibration testing and the single-degree-of-freedom vortex-induced vibration testing and comparing analysis results of the single-degree-of-freedom vortex-induced vibration testing and the two-degree-of-freedom vortex-induced vibration testing. Under the same testing conditions, the single-degree-of-freedom vortex-induced vibration testing along the flow direction or the transverse direction and the two-degree-of-freedom vortex-induced vibration testing along the flow direction or the transverse direction can be completed and synchronous measurement of hydrodynamic pressure, motion parameters (displacement, speed and acceleration) of a testing model and vortex discharge can be realized.