By the use of the WRF (V3.3.1) model and the assimilation system, experiments are carried out with the numerical simulation scheme designed on the different boundary and initial conditions with the different assimilated element observation. The sensitivity impact analysis of the WRF model boundary conditions on the simulation of the heavy rainfall happened in the eastern Sichuan Basin is discussed. The results show that the WRF model is sensitive to the change of initial and boundary conditions. The change caused by the assimilation of ground temperature is more sensitive than that caused by the assimilation of the ground wind field. The sensitivities to the upper level relative humidity, wind, and vertical velocity are bigger than those to the lower level. During test, the sensitivities to lower temperature and unstable energy are bigger than those to the upper. The sensitivities caused by boundary conditions increase with time. The sensitivities caused by initial conditions decrease with time.