In order to study the spatiotemporal evolution of the precursory anomalies 10 years before the Wenchuan M_S8.0 earthquake in 2008, the epicentral distance of the precursory anomalies is calculated by using the geometric center of the rupture region and the elliptical centerline of the aftershock region. The result shows, precursor anomalies gradually increased about 2 years before the Wenchuan earthquake. The ratio of abnormal items is greater than 25% in the near source area (about twice the source scale) and 17%-24% in the remote area (about 3-5 times the source scale). There are three different stages of spatiotemporal evolution of precursory anomalies. During the α stage (including α₁ and α₂, between 700 to 3000 days before the main earthquake), the anomalies are mainly distributed in the southwest and northwest area of the Wenchuan aftershocks area. It is shown that the precursors of the far source region and the near source area have the characteristics of outward expansion. During the β stage (between 300 to 700 days before the main earthquake), the anomalies are distributed in the southwest and northern region of the aftershock region, showing a large range of anomalies. During the γ stage (including γ₁ and γ₂, 300 days before the main earthquake), the range of anomaly distribution is wide, and the anomalies are distributed in the southwest and northeast of the aftershock area. The anomalies converged to epicenter (γ₁) in the far source region and expand outwards (γ₂) in the near source region.Results of the experimental study and mechanical analysis of earthquake preparation process indicate that the three-stage characteristics of precursory anomalies in the process of earthquake preparation may be controlled by the seismogenic body, which is a form of expression in the process of earthquake preparation and a universal feature during the earthquake preparation process, which has a certain guiding role in earthquake prediction.