This paper first considers the effects of multielectron interaction, L−S interaction and the weak crystal-field on the 4f3 ground state of Nd3+ ion in the paramagnetic medium NdF3; then, further takes account of the splitting of the crystal-field ground levels caused by both the effective superexchange field Hv and the applied field He, and calculates quantitatively the temperature dependence of the magnetic susceptibility χ in NdF3. For the splitting of 4f25d excited state of Nd3+ ion in NdF3, the paper investigates the effect of the strong crystal-field on the 5d electrons. Using the model of three-level transition, the specific Faraday rotation θF, the Verdet constant V, and their temperature dependence, which originate from the electronic transitions between the electron configurations 4f3 and 4f25d, are calculated quantitatively. The theoretical calculations show that the superexchange interaction between Nd3+ ions has an important effect on the magneto-optical properties in NdF3, and both V−1 and χ−1 are linearly dependent on T in the temperature range 70 K<T<300 K. The theory is in good agreement with the experimental results.