Abstract: This paper presents a comparatively thorough theoretical computation on the reactance and adimttance of four core square and triangular low voltage split insulated conductors at different sections and under different power supply modes, through the methods of computing electrical parameters of aerial lines and through electric and magnetic field theory.Compared with corresponding conventional aerial lines, this conductor possesses the features of lower reactance and higher admittance and per section flow of currents. The theoretical result from this computation is favourably consistent with that of experiments. And this computation method lays a strong theoretical foundation for the production and application of new low voltage split insulated conductors.Also it paves a way for forming new power supply modes in the reconstruction of electrical power networks.