Abstract: In order to study the main neutron absorber nuclides of the Ag-In-Cd control rods in the reactor and its effect on the control rod value, Monte Carlo method is used to simulate the burnup of the main nuclides in Ag-In-Cd control rods during the reactor operation, and the neutron flux in the control rod and the macroscopic cross-section are analyzed, to investigate the value of the control rods before and after irradiation. The results show that the nuclide ¹¹³Cd in control rods decreases sharply with the increasing of the irradiation time, while ¹⁰⁷Ag, ¹⁰⁹Ag and ¹¹⁵In decrease slowly; the macroscopic cross-section of the control rods decreases, while the macroscopic cross-section of ¹⁰⁷Ag, ¹⁰⁹Ag and ¹¹⁵In increase; the neutron flux in the control rods increases, hence the neutron absorber rates in the Ag-In-Cd equal to that in the no-irradiation control rods.