The study of flow field characteristics of free falling particle plume is part of the basic application research of gas-solid two phase flow. The Computational Fluid Dynamic Software FLUENT was adopted in this paper. The numerical simulation was carried out to study the influence of particle diameter and particle density to the particle flow field characteristics of free falling particle plume. The results of the numerical simulation showed that, with the increasing of particle diameter and the increasing of particle density, the disturbance of ambient air to the particle plume decreased, and the entrainment ability of particle plume to the ambient air was diminished.