A number of vertical line sources was generally caused by catalytic agents, dispersed from falling pyrotechnical flares of an airplane or a rocket. With the gradient-transfer theory of turbulent diffusion, we present a ther'otical model of agents diffusion of vertical line sources in supercooled stratiform clouds and, we give a calculative formula of superposing effect of agents' concentration of numerous vertical line sources, which were perpendiculor to the direction of horizontal wind or were parallel to the direction of horizontal wind.