The second order moment conservation and Bottadvection schemes that are responsible for being positive definite and high accurate are introduced into the MM4(meso scale model) for moisture advection.When separately used with the MM4 with observed windfields available a range of scenarios have been subjected to theoretical test and numerical experiments done with more than one rainstorm event.Nurnerical results show that the improvement of calculation accuracy of model moisture advection is the key link of raising the prediction of weather calamities like heavy rain.