Abstract: In order to realize the rapid on-site detection for pathogens in complex biological hazards，it is necessary to prepare a variety of biological samples，establish a multimodal biospectral database，and eventually achieve targeted rapid inactivation of pathogens.Ultrafine atomizer design is a key technology to prepare high-quality biological samples.The technology can atomize liquid biological samples into small droplets，and then the bioaerosol particles can be formed after low-temperature freezing and sublimation drying.Through the optimal design of the air-assisted atomizer，the ultrafine and uniform atomization can be obtained under the conditions of low flowrate and low pressure without damaging the biological activity.In this paper，the spray process was simulated by means of RANS+DDM method，and the atomization characteristics of the air-assisted atomizer were analyzed at normal temperature and low temperature with heating power.At the same time，LES+VOF method was also adopted to test the turbulence effect of gas swirling near the nozzle on the liquid fluidics，and the atomization mechanism was analyzed.Moreover，the atomizing effect of the air-assisted atomizer was tested by an aerodynamic particle size tester.The results show that the air-assisted atomizer has good atomizing effect and can realize ultrafine atomization of particles with a diameter of around 1μm.The quality of biological samples prepared by spray-freeze-drying method can meet the design requirements，so it can effectively prepare bioaerosol samples in mass quantities and improve the detection and defense capability for pathogens on the site of biological hazards.

Key words: air-assisted atomizer, ultrafine atomization, structural design, atomization simulation, turbulent breakup