It is well known that plasma beads are produced in the atmosphere by a focused high-power laser beam. The characteristics of propagation of a CO2 laser beam in the atmosphere including the plasma beads produced by focusing the laser beam were investigated. The optical air-breakdown mechanism was treated by empirical relations instead of taking inverse bremsstrahlung into considerations. A simple equation was newly proposed here to describe processes of growing of plasma beads. The simulated results on the density of plasma beads were qualitatively in agreement with experimental results. The model consisting of these procedures has a possibility to predict the density of plasma beads which are produced in the atmosphere by a CO2 laser owing to ignition of atmospheric aerosols.