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In this paper, by analyzing three-dimensional spatial and temporal variations of soil water content at two field sites, temporal variations of three-dimensional rainfall infiltration process in heterogeneous soil were studied. The three-dimensional soil water contents were obtained by soil moisture tomography. For eight rain events, the temporal variations of the homogeneity of the infiltration process were investigated. The results show that the three-dimensional rainfall infiltration process in heterogeneous soil varies with rainfall process. For rain events with short duration time and low rain intensity the infiltration behaves preferentially and heterogeneously. The preferential flow plays important roles in the conduction of soil water. While for rain events with long duration time and high rain intensity the infiltration shows more homogeneous characteristics. The preferential flow becomes less important. In a rain event, at the initial period of the rain, the infiltration process usually is a heterogeneous and preferential one. However, with continuing rainfall the infiltration gradually becomes more homogeneous and plug-like.