The heat produced by U and Th is the main energy that leads to the evolution of the planets. At the same time, the radioactivity of U and Th also has an important effect on living beings. So it is necessary to probe the geochemical behavior of U and Th to understand the evolution history of the planets , the origin and evolution of the Earth' s crust and the evolution of living beings. In this paper, the authors have reached the following conclusions: 1. According to the physical and chemical properties of U and Th, it is considered that there are two different ways in their migration. (1) In the rocks containing volatiles with oxidation ability, such as H2O, O2, N2, F2, Cl2or their ions, the U and Th will combine with them chemically to become high valence compounds and complexes, which have an intense tendency of migrating from high to low temperature facies by magmatism and metamorphism. Because there are a lot of volatile with oxidation ability in the Earth, such as H2O, O2, N2, F2,Cl2or their ions,most of the U and Th migrat directly or indirectly to the zone of enrichment (ZE) under the lithosphere first, and then to the crust. (2) In the rocks without volatiles or with volatiles having no oxidation ability, the U and Th will exist in metal or low valence compounds with high melting point and high density. In that case, the U and Th are stable and reluctant to migrat. So in the planets without volatiles in the interior near the Earth's core, the U and Th will sink down to their center. 2. The unique evolution history of the Earth is closely connected with the properties of U and Th mentioned above and its volatiles. Because of the participation of the volatiles in the migration of U and Th ,most of the U and Th in the interior of the Earth migrat to the ZE first,then they heat the rocks to melting . So the rocks in the ZE are plastic, which causes the mantle convection and the drift of continents. It is the U and Th enriched in the ZE that drive the global crust movements, especially the plate movements. Without volatiles with oxidation ability , there would be no ZE in the planet. Without the ZE, there would be no the plate tectonics in the Earth. In the Earth's core, these U and Th also can be driven to the ZE by the upward plumes when they are changed into high valence compounds and complexes in the core_mantle boundary by combining with H2O, O2, N2, F2, Cl2or their ions that come from the mantle,subduction plate and down plumes. In the other planets, because of the lack of volatiles with oxidation ability, there are no ZE like that in the Earth, and there are no the plate tectonics in their crusts either. Also because of the participation of the volatiles in the migration of U and Th in the early stage of the Earth, the contents of U and Th in the ZE reach their highest values, then decrease with time. Correspondingly the intensity of global crust movements decreases with time, which is advantageous to the evolution of living beings. But in the planets like the Mercury and Mars which have no volatiles or like the Venus which have only little volatiles with oxidation ability, most of U and Th will sink into their cores first, then they heat their cores to melting facies and the melting facies enlarge with time. At last, they may reach the position like the ZE in the Earth and then lead to the mantle convection and drive the global movements. So their evolution are slowed down because of the lack of volatiles. Or the heat in their center is sent to their surface only through intense volcanic activities as what occurs in the Mars. The intensity of the global geological activities in these planets increases with time, which is contrary to things in the Earth. 3.The migration of U and Th from the ZE to the Earth's surface varies with time. In the early stage, the increase of U and Th in the Earth's crust is very quick due to the intense volcanic activities, large dose X-ray from the U and Th can destroy the DNA of living beings and is dangerous to them and restrain the development and evolution of living beings. After the Phanerozoic eon, this kind of increase of U and Th is slowed by changing the migration way from intense volcanic activities to plate movements, the small dose X-ray can not destroy the DNA of the living beings, and is not harmful to life but may cause a small change in the gene structure of living beings and become a resource to lead to the diversity of living beings and the biological evolution.