Abstract: The properties of microparticles are almost closely related to the particle size. In order to study the characteristics of aerosol particles, it is necessary to obtain particle size distribution information. The inertial impactor is a device based on the principle of inertia to realize the deposition separation of particles of different sizes in the atmosphere. During actual use, it experiences complex and changeable environments. In this paper, the Lagrangian multiphase (LMP) model is used to numerically simulate the gas-solid two-phase flow in the impactor. The effect of aerosol temperature variation (−40 °C ~ 60 °C) on the particle deposition rate was investigated using the finite volume method (FVM) under both adiabatic and heat transfer conditions, and its effect on particle size separation was analyzed. The results show that: under the condition of wall adiabatic, as the temperature of the aerosol increases, the particle deposition position diverges from the center of the impact plate to the edge, the particle collection efficiency decreases, and the number of particle collection decreases gradually; in the condition of aerosol and wall heat transfer, as the temperature of the aerosol increases, the deposition position of large particles diverges from the center of the impact plate to the edge, and the collection efficiency of particles decreases, while the opposite is true for small particles. In addition, there is an intersection point in the particle collection efficiency curves at different aerosol temperatures, and the collection efficiency of large and small particles on both sides of the intersection point changes oppositely with temperature. By studying the influence of temperature on the impactor particle collection, the results of particle diameter separation can be modified and more accurate particle size distribution can be obtained.