When concentration of free nitrogen in initial ammonium tungstate solution increased from 17g / L to 51g / L, the bulk density of the resulting APT decreased from 2.22g / cm3 to 2.02g / cm3. Since the content of free nitrogen is high, PH decreases slowly during evaporation and crystallization. The solution concentration increased with time, when the solution reaches the paratungstate PH range, the oversaturation of solution increases, so the resulting APT particle size is relatively reduced. If continuously add a amount of free ammonia to the solution during the crystallization process, PH of the solution can be maintained within a certain range, so that the oversaturation of solution is controlled, which is conducive to particle growth.