Aggregates are the basic units holding plant-available water and keeping the soil permeable. Objectives of this review are to highlight soil aggregating-factors, which are basic knowledge to soil management through discussion around aggregate-forming theories. This review firstly summarized the three main aggregate-formation theories: clay domain theory of Emerson, micro-aggregates theory of Edwards and Bremner and the hierarchical theory of Oades and Waters, then discussed the roles of organic matter, soluble salts and sesquioxides in aggregation of soil particles, thirdly analyzed the mechanism of aggregate slaking and dispersion and their main evaluating methods, and eventually indicated that keeping soil particles in aggregated state and increasing the soil organic matter of different types had been the main measures to increase the degree of aggregation.