We developed the model equations to investigate the particle movement and growth theoretically in a-Si plasma CVD reactor, where those particles act as the source of contamination. We included the effects of fluid convection, particle diffusion and external forces (ion drag force, electrostatic force and gravitational force) onto the particles to analyze the movements of particles in plasma reactor. Taking into account the particle charge distribution, the particle growth by coagulation between the charged particles was investigated. Most of those particles are located in the region near the sheath boundaries by the balance between the ion drag and electrostatic forces. The particle concentrations in the sheath region and in the bulk plasma region are almost zero. The sizes of the predator particles increase with time by the coagulation with protoparticles and, as a result, the surface area and the average charge of predator particles also increase with time.