Abstract: Critical experiments on the four fission products including Ag, Sm, Gd and Nd were conducted on uranyl nitrate solution experiment facility. The fissile material of the core was solid-liquid two-phase, solid fuel was uranium dioxide and liquid fuel was uranyl nitrate. The fuel rods were arranged in hexagonal lattice, and were soaked in uranyl nitrate solution. The results of the critical experiment were compared with those of the Monte Carlo code MONK. The theoretical calculation results are in good agreement with the critical experimental results. The negative reactivity worth introduced by the fission product sample is considerable and the spectrum change shows that the absorption of neutrons by the fission product sample plays a conclusive role in the energy region below the thermal energy point.