Abstract: On the basis of physical mechanics of the turbulent diffusion, the turbulent diffusion process has been described with Ito's stochastic differential equation, and the concentration model of the continous point source has been obtained. Its first order approximate solution has been expressed as a form of analytical function. The special cases of the first order approximate solution has been identified with the form which has been commonly used. The solution includes the factors of geostrophic wind, gravity deposit and etc., which influence the diffusion process certainly.