The electromagnetic field finite element numerical model of the reactor, considered the hysteresis effect of the ironcore, was derived by combining the JA model and the numerical analysis method. The electromagnetic field distribution of the reactor was analyzed by using the two methods of single value basic magnetization curve and hysteresis loop, respectively. The results showed that the magnetic hysteresis had a great influence on the calculation results of the electromagnetic field distribution of the reactor. The electromagnetic field computing model considering the hysteresis effect of the ironcore lays a foundation for further research on the reactor heat.