From more than three hundred experiments we have confirmed that the physicochemical conditions of formation of globular uraninite are variable in a wide range and put forward a new mechanism of itsl formation. U308 is not a transition product during the synthesis of gobular uraninite. When pyrite reduces UO2+2 to form globular uraninite, the valence state of Fe and U has a synchronous relationship both in growth and in decline. Hematite and glob- ular uraninite are two products of different stages in process of evolution, and the former precipitates-earlier than the latter. The globular thorium-bearing uraninite crystallises out within the range of 150-200℃·Thorium is substitu- ted in the form of isomorphism for U0* in crystal lattice. The thorium content of globular thorium-bearing uraninite increases with the strengthening of reducing field.