Abstract: For a large wind farm cluster, both the spatial-temporal varied wind speed and the spatial dispersed sites of wind farms in the area of the cluster cause different power waveforms of wind farms. Although the power waveform of wind farm cluster is composed by all power waveforms of each wind farm, the former will present some evolutionary properties, such as lower relative power fluctuation than that of single wind farms. This phenomenon is defined as the Cumulative Effect of the power fluctuation of wind farm cluster. In order to reveal the mechanism of cumulative effect and its factors, a one-dimensional travelling wave function of wind speed is derived to approximately describe a time varied wind speed along with the dominant wind direction in the area of the cluster, and the amplitude-duration coupling characteristics is established based on the wavelet transformation to reveal the temporal characteristics of power waveform of single wind farm. The cumulative model is derived by a single wind farm power waveform as the representative and correlated to other power waveforms. Based on the cumulative model and the amplitude-duration coupling characteristics of single wind farm power waveform, the evaluation method of cluster power fluctuation range is derived. By using this method, the power fluctuation evolution mechanism is soundly revealed both spatially and temporally. The validity of the proposed model and analysis method is verified by 2 real wind farm cluster cases as examples.