Fine ammonium paratungstate was prepared by microwave-ultrasonic cooperative evaporation crystallization without external force or any surfactant. The effects of temperature, ammonium tungstate concentration, power of microwave and ultrasonic, as well as cooperative time on the particle size and morphology of ammonium paratungstate were investigated. Under the optimum conditions, the fine single-crystal ammonium paratungstate with an average particle size of 7.6 μm, uniform size distribution, perfect crystal, and five crystal water could be prepared.