Abstract: A simulation of the heavy rainfall process along meiyu front was conducted using the NCAR/PSU mesoscale model with a four-dimensional data assimilation. The model output of high temporal and spatial resolution was used to investigate the uneven characteristics of the structure of meiyu front, which was closely responsible to the heavy rainfall. The results indicate that the meiyu front consists of two segments vertically, the middle layer front and boundary layer front. The vortex and associated heavy rainfall along meiyu front were more sensitive to the middle layer front than to the boundary layer front. The intensified, steeper of the middle layer front and intensification of the vertical circulation across the frontin the middle layer are favorable to the later enhancement of precipitation along the meiyu front. The peak intense of prcipitation did not occurred at the same time while the middle layer front reaching its peak intensity, but the former has a lag of about 16-24 hours. The total deformation fields at middle and low layer were closely associated with the development of front. The distribution and evolution of u and v components were significant different. The southerly jet stream center was at 900-800 hPa, and the strong westerly flow was at middle level of 700-500 hPa ahead of the front, appearing as the downward extension of upper level westerly along the upper boundary of the front. The vertical saturated warm moist air column, southerly low layer jet and westerly middle level jet ahead of the front show highly organized features at the intense front segment. Some low layer fields along Meiyu front, such as convergence, front intensity, deformation and southerly wind, show evident mesoscale orographic features and with significant daily variation.