A numerical study for representing time-dependent natural convection of Czochralski melts, while the growing crystal and crucible do not rotate, is presented in this paper. Using a finite control volume algorithm with central-diference discretization of advective and diffusive fluxes, the Czochralski flow which is governed by the rwo-dimensional N-S equations based on Bous-sinesq approximation is computed. The calculations present some interesting streamlines and isotherms with typical time, total kinetic and thermal energy as function of time. The time-de-pendent transport phenomena in Czochralski melt extend into oscillatory for Gr = 1.6×106 in Pr=0.015. This results obviously influence the thermal fluxes at the crystal-liquid interface. The unsteady simulation in this paper is much helpful for the recognition of natural convection and actural crystal growth in Czochralski melts. The program are also available to other models of Czochralski crvstal growth.