In the present work, magnetoresistivity performance of polycrystalline Bi2Sr2Ca1-x K (x) Cu-2 O (8+y) superconductor with x=0.0,0.05,0.075, and 0.1 has been studied by change of flux pinning mechanism, using magnetoresistivity measurements. The samples were prepared using a polymer solution technique. The effects of K substitution for Ca on the irreversibility field, upper critical magnetic field, coherence length, and activation energies have been investigated. The magnetoresistivity of the samples has been measured under applied magnetic fields ranging from 0 to 9 T. Broadening of superconducting transition is observed under magnetic field, explained on the basis of thermally activated flux flow (TAFF) model. The upper critical magnetic field H (C2)(0) and the coherence length (zeta(0)) at T = 0 K were calculated using the resistivity data and from H (C2)(0) ,respectively. H (C2)(0) and xi(0) values have been calculated as 62, 72, 75, and 53 T and 23, 21, 20, and 25 for the 0.0, 0.05, 0.075, and 0.10 K doped samples, respectively. TAFF model has been studied in order to calculate the flux pinning energies. In particular, the flux pinning energies of Bi2Sr2Ca1-x K (x) Cu-2 O (8+y) where x = 0.075 are calculated as 0.0147 eV for 9 T and 0.29 eV for 0 T.