The general equation that describes the AC magnetic susceptibility response of the superconducting system due to the change of varying AC field H ̇ = dH dt has been reviewed. By using the AC susceptibility measurements, the temperature, magnetic field and current density dependence of the effective pinning potential U(T, H, J) for our Pb-doped Hg-1234 superconductor has been determined. It is found that the fast drop of the effective pinning potential with current density is due to the large value of the characteristic exponent μ which depends on the existing types of non-superconducting phases that form the intergrowth structures with the dominant matrix. The characteristic curve of electric field E(J) against the current density J has been obtained from the AC susceptibility technique. For consideration of current relaxation due to the presence of giant flux creep, we have studied and determined the temperature dependence of the critical current density J c for our specimen.