A mathematical model describing the behavior of evaporating solution droplets in spray pyrolysis was developed and verified. The effects of mass, momentum, and heat transfer, as well as solute precipitation, on evaporating solution droplets were considered simultaneously. The concept of real solution was used in calculations to estimate the saturated vapor pressures of the droplet. The precipitation heat of solute caused the droplet temperature to jump up and enhanced the solvent evaporation rate. While increasing the gas temperature resulted in a steeper concentration gradient inside the droplet, decreasing the concentration of the starling solution reduced the sizes of resultant particles. Accordingly, a two-stage heating arrangement with a dilute starting solution in spray pyrolysis is suggested to produce small solid aerosol-derived particles.