In recent years, haze has become a new type of environmental disaster, it is also one of the most disturbance factors in remote sensing image. Now, to study the influence of haze on electromagnetic waves has got more and more attention. In this paper, the definition of haze and composition of PM<sub>2.5</sub> particles were introduced. And based on Mie scattering theory, the extinction characteristics of single and mixture of PM<sub>2.5</sub> particles with different size and refractive index were analyzed. The calculation shows that the extinction efficiency factor of single PM<sub>2.5</sub> particle changes with the different particle size and refractive index, the oscillation of extinction curves become obvious with different particle size in the case of weak absorption, when it is strong absorption, this phenomenon will disappear. At the same time, based on the study of extinction efficiency factor for single particle and the equivalent method, it is found that the extinction efficiency factor of a lot of particles increase rapidly with the change of particle sizes, then, it will decrease and tend to a constant. The factor is also associated with the change of the width of particle size distribution and refractive index, usually not monotonous. For external mixture of particles, the extinction curve also relates to the mixing ration for the mixing particles. Because there are many mixture of particles in reality, the study of characteristics of extinction efficiency factor in this paper is significant for the research on the optical characteristics of PM<sub>2.5</sub> particles in practice.