The resistivity related to temperature and magnetic field is a crucial parameter for determining the physical properties of the perovskite-type manganese oxide. The first task of this work is to find out a suitable method to predict the resistivities of La0.67Ca0.33MnO3 and Pr0.7Sr0.3MnO3 in the process from insulator phase to the metal phase via the temperature and the magnetic field. Based on the nonlinear numerical fitting, an analytical expression showing the dependence of the resistivity on temperature both less than and higher than the metal-insulator transition Curie temperature (TC) at different magnetic fields, and the maximum resistivity (ρmax) corresponding to each Curie temperature is acquired. The second task of this work is to trace a mathematical relationship between the magnetic field and the maximum resistivity, and the Boltzmann function can be used successfully by numerical fitting. The lowest correlation coefficient and the largest average relative error between the actual and the calculated data are 0.998 and 4.35% in all considered cases respectively.