In this study, the reduction-carbonization property of WO3 obtained by thermal decomposition of ammonium paratungstate (APT) under N-2 and air atmosphere in a fluidized bed was investigated. The decomposition property of APT in N-2 and air was analyzed by TG analyzer. Phase, morphology, deoxidation rate and carbonization rate of the decomposed products in the reduction-carbonization process were investigated. It was found that APT could be rapidly decomposed into monoclinic WO3 in a fluidized bed in Ny or air atmosphere. Compared with N-2 atmosphere, air was more favorable for the rapid decomposition of APT and the crystal transition of WO3. Under the same conditions, the products obtained in N-2 atmosphere had smaller grain size, larger porosity, faster deoxidation rate and carbonization rate. Both WO3 obtained in the N-2 and air could be reduced and carbonized to nano-sized WC with SBET particle sizes of 63.70 nm and 73.49 nm in a fluidized bed, respectively.