and dehydrated air as a fluidizing gas is introduced to the bottom of the apparatus 5 through a pipe 13 the operating temperature is less than 200 u00b0 c preferably in the range of 100 u00b0 c 180 u00b0 c the dried and dehydrated particles are overflown from the upper part and sent to a third fluid bed reaction apparatus 6 where the particles react with steam as a reaction gas and a fluidizing gas introduced to the bottom of the apparatus 6 through a pipe 14 to form uo 3 or u 3 o 8 this uo 3 or u 3 o 8 is similarly overflown from the upper part of the fluid bed to be sent to a fourth fluid bed reaction apparatus 7 where the uo 3 or u 3 o 8 reacts with a mixed gas of steam and hydrogen gas as a reacting gas and a fluidizing gas introduced into the bottom of the apparatus 7 from 15 to form uo 2 the uo 2 powder is received as a product by a container 8 this operating temperature is less than 700 u00b0 c preferably in the range of 500 u00b0 c 600 u00b0 c in consideration of activity of the uo 2 powder 16 is a waste gas treatment line 1 the uo 2 powder obtained has a high activity a small remaining fluorine quantity and excellent fluidity such uo 2 powder as that of the present invention can not be obtained by conventional process 2 the excellent fluidity of the uo 2 powder can make handling thereof in following steps very easy and can.