Abstract: Core design for radioisotope production in pressurized water reactor (PWR) nuclear power plant was carried out. Cobalt rod replaces thimble plug rod. 24 cobalt rods were symmetrically suspended under the new design thimble plug assembly to produce radioisotope under the premise of ensuring the safety of the reactor. In this paper, the design of cobalt pellets, cobalt rods and cobalt target assembly was described in detail. The characteristics of cobalt target assembly and its influence on the core loading pattern design were analyzed. The results show that the cobalt radioisotope production by PWR is feasible in core design. The core safety parameters meet the requirment of limit values, and the production of radioactive sources can bring good economic benefits to the nuclear power plant.