The exchange interaction-effective field in PrNi₅ is given as $H_{in}=a{H}_e+b{H}_e^{3/2}+c{H}_e^2\text{.}$

A set of method for directly calculating the Zeeman Hamiltonian is given.

The magnetic entropy changes of PrNi₅ are calculated in 0<H_e<20T$0<H_e<20T$ and 2<T<60K$2<T<60K$.

The most relative error of magnetic entropy changes reduced from 59.8% to 24.5%.