The work aims to investigate the particle size distribution in the soy protein liquid atomization field and the influence of spray parameters on soybean protein liquid atomization droplet size in the process of spraying, thus to choose the optimal spray parameters in the process of preparing coated vegetable composite paper. Particle size distribution in atomization field of soybean protein liquid was measured under different spraying parameters by using laser particle size instrument, and the effects of spraying parameters on atomized particle size of the soy protein liquid was analyzed through the data analysis software Origin. When spraying parameters were certain, atomized droplet diameter of soy protein liquid significantly reduced before they were stable with the increase of axial distance in the spray atomization field. Soy protein liquid droplet diameter at the same axial location of the spray atomization field showed a trend of decrease with the increase of radial distance. Soy protein liquid droplet size at the same test point of spray atomization field decreased with the increase of spray air pressure. Impact of spray hydraulic pressure on soybean protein liquid droplet size was not significant. In conclusion, the soy protein liquid droplet size in the plane 30 cm from the nozzle in spray atomization field is smaller and more uniform when the spray air pressure is 0.2 MPa and the spray hydraulic pressure is 0.16 MPa.