The magnetic properties of some magnetic materials are influenced by the exchange interaction between magnetic ions and the spin fluctuations of magnetic ions. By use of the exchange interaction-effective field including the spin fluctuations of magnetic ions Hm= n0(1+γ T +β eω T)M, the Zeeman splitting of crystal field energy levels of Pr3+ ions in PrNi2 and the variation of the magnetic moments with the applied field in a temperature range of 3.8 K≤ T ≤ 30 K are calculated. The thermal variation of the reciprocal susceptibility of Pr3+ ions is calculated as well for the applied magnetic field H=5000 Oe. The calculated results are in good agreement with the experimental data. The magnetic entropy changes are obtained theoretically in a magnetic field range of 0H<50000 Oe, and the results are similar to those reported in the literature. It is indicated that the exchange interaction-effective field containing the spin fluctuations is applicable not only to the ferrimagnetic crystals, but also to the paramagnets.