Abstract: The paper has established an equivalent-circuit model of the four-level-coaxial-circular-cone-like magnetically insulated transmission line of PBFA Z by treating its vacuum section as several pieces of lumped inductance in terms of its magnetic insulation properties. The model has incorporated magnetic insulation theory, space-charge-limited flow theory, Mendel's MITL pressure balance equation, and wire-array implosion dynamic model as well as several critical geometric parameters of the MITL. The comparison of calculated results of a typical PBFA Z test by the model with those by other models and measured results indicates that the model be valid and can be used as a convenient tool to design and estimate similar MITL configurations.