The non-balance wind (difference between real and balance winds) is decomposed, into divergent and rotational components. The dynamical impacts of these two components on the development of heavy rainstorm are analysed. It is found that the rotational part plays a role in maintenance of the divergent field.Three experiments with differential initialization methods are carried out by using a 5 level limited area model. The precipitation forecast is improved if both the divergent and rotational components are included in the initial wind field.