Several hypotheses about soil aggregate were suggested from the researches in the past 30 years. The author carried out further experiments in order to verify them from 1998 to 2003. The theories derived from those hypotheses are as follows: (1) It isn't possible to declare that the total amount of soil aggregate (water-stable and non-stable ones) is constant but the change of its quantity is very small. (2) It is probable that the water-stable aggregate is formed after the organic matter in the sil dried up. But it is insufficient to express the relation among these factors quantitatively by the multiple regression equation. (3) Continuity in the same field is admitted to the theories about soil aggregate but universalism among different fields isn't admitted.