Based on the constitutive relation between the magnetic permeability and magnetic flux density, the constitutive relation of magnetized ferrite medium in frequency domain is transformed to the time domain by using the corresponding relation between the time-differential operator /t and jω. And the constitutive relation including the time-differential operator /t in time domain is presented. By the introduction of a direct-discrete method, the time-differential operator /t is dispersed. Then direct discrete-finite-difference time-domain(DD-FDTD) iterative formula are derived in the discrete time domain. To exemplify the availability of the algorithm, the backscattering radar scattering section of a magnetized ferrite sphere is computed, and the numerical results are the same as the reference values, and show that the DD-FDTD method is correct and efficient.