Abstract: The development of symmetric disturbances superposed on the background field of Hoskins-Bretherton (1972) frontogenesis model is investigated by using the WKBJ approach.It is found that the forcing of large scale deformation,the frontal circulation and the variations of stability parameters (F2,N2,M2) can induce the development of symmetric disturbances even though the frontal baroclinic flow is symmetric stable (F2N2-M2=q0).The frontogenetical process of deformation confluence and the ascending branch of frontal circulation are in favor of the development of symmetric distur bance.The actions of ageostrophic shear in frontal zone and the variation of stability parameters are dependent on the structure of disturbances.