We performed a numerical simulation of the trapped field properties of MgB 2 bulk disks with different superconducting characteristics magnetized by field cooling. The temperature dependence of the trapped field B T () z , and the time dependence of the local field B t () z and temperature T (t) were calculated, and compared with experimental results. Since the measured critical current density J T B (,) c was used in the simulation, the results of the simulation reproduce the experimental results well. These results suggest that the value of B z and the trapped field profile can be estimated precisely for bulks of any shape and under any conditions, such as the operating temperature and applied field, using the measured J T B (,) c characteristics. The diameter and thickness dependence of B z was also calculated.