Beer-Lambert model is a relation concerning the absorption of radiant energy by an absorbing medium. In this paper,
we modified the Beer-Lambert model to investigate the penetrating magnetic field behavior in a superconducting shield by taking
into account the effect of a power-law term of previous penetrating magnetic fields internal materials. The penetrating fields were
derived analytically and applied to cylindrical MgB2 superconductors. We found that our calculation results of penetrating field
fit well with experimental data of cylindrical MgB2 superconductors in the range of 0.1-0.6 T