The present paper is an attempt to construct an extended Harris-Todaro Model —— an equilibrium model that incorporates a stochastic fluctuation. Based on this stochastic dynamic Harris-Todaro Model, we examined how an increase in the demand fluctuation and the ratio of less productive producers effects migration and welfare. The results revealed that an increase in uncertainty of demand and a decrease in the ratio of less productive producers enhance both the growth rate and variance of the urban employees as well as welfare.