For studying the influence of the thunderstorm electric field intensity and the length of the nylon wire which isolates the conductor from the ground on the success rate of artificially altitude-triggered negative lightning,a 3-dimensional numerical model of artificially altitude-triggered negative lightning is developed with a space resolution of 50m,based on an analytic thunderstorm model and the Dielectric Breakdown Model(DBM).And some area near the conductor with a strong electric field is detailed to a resolution of 5m with the interpolation method.