The evolutionaI processes (development, propagation and the change in structure) of Rossby way epacket in the forced barotropic or baroclinic mean flow are investigated by using the WKB method in this paper. It is concluded that (ⅰ) a growing wave packet enlarges its mean spatial scale but the decaying one shortens its mean Spatial scale, (ⅱ) barotropieally growing disturbance propagates toward the jet axis but the decaying one out from the jet axis on the horizontal surfaces, (ⅲ) baroclinically growing disturbance propagates toward the jet axis but the decaying one out from the jet axis in the vertical, (ⅳ) the development characteristics depend on the structure and the location related to the mean flow, (ⅴ) the forced stationary wave train has the structure typical for the baroclinically growing but barotropically decaying disturbances, propagates toward tropopause but out from the jet axis on the horizontal surfaces, and splits up into two branches in propagation if the forcing is located near t The evolutionaI processes (development, propagation and the change in structure) of Rossby way epacket in the forced barotropic or baroclinic mean flow are investigated by using the WKB method in this paper. It is that that (i) a growing wave packet enlarges its mean spatial scale but the decaying one shortens its mean Spatial scale, (ii) decaying one out from the jet axis in the vertical, (ⅳ) the development characteristics depend on the structure and the location related to the mean flow, (ⅴ) the forced stationary wave train has the structure typical for the baroclinically growing but barotropically decaying disturbances , propagates toward tropopause but out from the jet axis on the horizontal surfaces, and splits up into two branches in propagation if the fo rcing is located near t