Thorium-bearing pitchblende (U4+(0.68)U6+(0.27)Th4+(0.05)O2.27. is a variety of pitchblende discovered in China, and it is an important primary economic uranium mineral. The main difference between thorium-bearing pitchblende and pitchblende is the high ThOz content (1.79-10.03%)and high Th : U ratio ( 0.02-0.14 ). and it is similar to pitc}ablende in other chemical and physical properties. At medium-low temperatures, when ore solution has soufficient F-1 concent- ration which forms fluoride and complex compound with uranium and thorium, uranium and thorium can migrate together in the same solution. In the process of ore formation, uranium and thorium can not separate completely but preci- pitate together, because ore solution is rapitedly cooled. The discovery of tho- rium-bearing pitchblende indicates that the isomorphism replacement of uran- ium arid thorium not only takes place at high temperatures but also does under the conditions of medium-low temperatures.