Abstract: In the general parameterization models of hailcloud the intercept of size distribution of hydrometeor particles were defined by a constant so that the natural evolution between cloudwater and raindrops and between raindtops and hailstones was seriously distorted. In order to improve the model we have removed this restriction by introducing the equations of concentration continuity for raindrops, frozen raindrops and hailstones and proposed a new formula of the size distribution. On this basis we have derived the formula of production term for eachequation and obtained a new parameterization model which may better discribe the interactions among various kind of hydrometeor particles. The model is one dimensional and time-dependent. The results computed from this model indicated that the physical feature is improved obviously.