The addition of base station antennas makes the scattered field of a shared tower more complicated

and the discontinuous scatterers have a coupling effect under multiple excitation sources

and further change the boundary conditions used in the derivation of the electric field integral equation in the traditional transmission line passive interference solving algorithm. For this reason

based on the generation mechanism of the passive interference scattering field of transmission lines

the coupling effect between the discontinuous electromagnetic scatterers is taken into consideration

and an algorithm based on the large elemen-physics optic（LE-PO） method to improve the solution for passive interference level of shared towers is proposed. Based on the reciprocity theorem and the principle of equivalence

the boundary conditions after the second-order coupling scattering of the shared iron tower scatterers are derived and are solved simultaneously

and the equivalent sources of the scatterers under the background of mutual coupling are obtained. The source performs an integral solution to obtain the scattered field of the shared iron tower

and finally achieves an accurate solution of the passive interference level. The experimental verification of a single base station antenna and a single iron column anechoic chamber shows that the relative error of the passive interference solution method considering the coupling is 2.62%

while the relative error of the traditional LE-PO algorithm is 9.85%.