Abstract: A semi-spectral model of global primitive equation is used to simulate the cross-equator propagation of quasi-stationary planetary waves.The results show that the amplitude fluctuation and phase variation of the quasi-stationary planetary waves at the tropopause in winter can cause the cross-equator propagation of the planetary waves in the middle atmosphere and create the transient planetary waves in the summer hemisphere.A new mechanism that the cross-equator propagation of the planetary waves in the middle atmosphere and the source of the planetary waves in summer hemisphere and the coupling between northern and southern hemispheres was advanced by the simulation.