Abstract: It is well known that the accumulation of liquid hydrometeor is very important for large hailstone's formation, but there are some uncertainties for accumulating mechanism of hydrometeor particles. Therefore the mechanism of accumulation is re-simulated by use of 3D- Euler model for macro and micro cloud fields and 3D-Lagrange growth travel model for the behavior of hydrometeor particles, following results have obtained: (1) Due to the airflow field is convective there is a dynamically attractive region located by the main updraft and here the horizontal velocity of airflow is near by zero, the particles may come together here, and then the accumulation occurred. (2) The accumulation is controlled by the interaction between the airflow field and the behavior of particles growth-travel, the accumulation of particles without growth is impossible. (3) The accumulation or convergence of particles is cyclic and developmental, the particle may entry the accumulation region or run out in process of accumulation. (4) The accumulating process is controlled by airflow and particle's behavior, but the accumulation of particles is of liquid(rain drops) or solid (snow、graupel or hail) that is cont rolled by the cloud-precipitation micro-physics. (5) The depletion of cloud-water or rain-water occurred in accumulation region mainly. (6) When the content of cloud-water is 6.0 g/kg and the concentration of particles is over 100.0/m3 the final size of particle is below 1.0 cm during the growth-travel.