Abstract: The divergent bcrotropic vorticity equation has been uscd in the 500 mb forecasts for Eurasia.The result shows that the movement of presure systems obtaincd from this model is slower than that of actual case.It is estimated that this phenomenon is firstly due to the unsuitable choise of the mean level adopted in this barotropic model,and sccondly due to the effect of the factor which controls westward movcmcnt of the ultralong waves。Finally an improved barotropic model is proposed.