Abstract：Using the WIMS & CITATION program, a neutronic parameter calculating model for the IHNI-I (In-Hospital Neutron Irradiator Mark I) reactor is presented in this paper. In the calculations of the cell group parameters, the bundle model is adopted. The control rod, the top Be reflector, the bottom Be reflector, the side Be reflector and each circle fuel rod of the core are taken as different cell types. In the whole core calculation, the R-z model is adopted by using the CITATION code. The power distribution, the reactivity worth of the control rod and the top beryllium, the temperature coefficient and the burnup are calculated. It is shown that the results agree with the values in literature, and the method is appropriate for the physical calculation of the IHIN-I reactor.