Abstract：With the increasing concerns for ecosystem functioning and services provided by soil, the study on soil aggregates has been increasingly a streamline discipline of modern soil science with the continuing updating of consensus and the methodology. In this review, we provide a holistic overview of understanding and characterizing soil aggregate system emerged for over last two decades. Evolution of concepts of soil aggregation, size fractionation and structural characterization is displayed, and separation and examination of the biophysical structure are discussed, as well as the final core scientific consensus of soil hierarchy system is synthesized. The main point of view of understanding soil aggregates include the followings. ① Soil aggregates are considered as the minimum micro-architecture and functional units, comprised of mineral particles, organic matter and (micro-) biome via their interaction and co-occurrence, thus noting their basic functional particles of soil in nature; ② The micro-spatial distribution of soil aggregates at different hierarchy levels results in the heterogeneity but functional diversity of a soil; ③ The final nature of soil aggregates could be envisaged of the embedded bio-pore system, created via the dual structure of aggregate and the associated pore system governed by the hierarchy aggregate system; ④ A soil aggregate system is generally represented by the three major hierarchies of aggregate size fractions including macroaggregates, microaggregates and silt/clay fraction, with the macroaggregates formed via binding microaggregates and/or silt-clay particles with coarse organic matter in a mode of pomegranate; ⑤ Wet sieving of field moist samples are recommended for preparation of soil aggregate separates despite of dry or moist sieving often used for samples from dry lands; ⑥ The μCT tomography technology is a powerful tool to quantify and visualize the pore system of soil aggregates, potentially linking to soil life processes and ecosystem services. Global cooperation is urged to develop unified protocol for fractioning, quantifying and visualizing the soil hierarchy system of aggregates of world soils. With the developments, the complexed soil system, particularly of the biodiversity of soil, can be explored at aggregate scale. Based on the updated understanding and characterization of soil aggregate system, nature-based solutions for global soil management policy and technical options will be provided for developing Earth sustainability.