Abstract: Electromagnetic field theory and electron motion conservation equations are used to derive numerical model of transverse spacecharge flow and magnetically insulated critical condition in conical transmission lines. Through numerical calculation, we have discussed the influence of the voltage and the cone's geometrical parameters on the transverse spacecharge flow and magnetically insulated performances. The higher the voltage is, the larger the spacecharge flow without magnetic field, and the better magnetically insutated performances. The geometrical factor K in the three geometrical parameters of the lines has the greatest influence on the transmission performances.