The Region-Time-Length (RTL) method was adopted in analyzing the characteristics of the seismicity changes prior to the Ms8.0 Wenchuan earthquake occurred on May 12, 2008. After the pre-analyses (completeness analysis and aftershock declustering) of the earthquake catalog in China, the RTL parameters in the investigated region were calculated. The temporal variations of the RTL parameters at the epicenter of the Ms8.0 Wenchuan earthquake showed that a seismic quiescence anomaly appeared during 2006–2007. The close investigation indicated that the above quiescence anomaly is unlikely an artifact due to the selections of the model parameters. The investigation of the spatial distribution of seismic quiescence also showed that the quiescence anomaly appeared around the epicenter of the mainshock during 2006–2007, consistent with the results obtained from the temporal variations of the RTL parameters. The above characteristics of the seismicity changes may give better understanding of the seismogenic process of the Wenchuan earthquake.