Abstract: Ag-In-Cd control rods are widely used in PWR nuclear power plants. The irradiation swelling behavior of Ag-In-Cd alloy is very important to the safety assessment of control rod during its operation. In this work, to simulate the change of microstructure and density of Ag-In-Cd alloy after irradiation in reactor, a series of simulation alloys were prepared, and the effect of composition on the microstructure and density was investigated. A formula to calculate the alloy density with different compositions was obtained by fitting the experimental values. It is found that simulation alloy will consist of two phases, an fcc phase and an hcp phase, when the content of Ag was 77.5% (mass fraction). In the fcc phase, Ag content will be higher than its average content, and there is a little amount of Sn. In the hcp phase, Ag content will be below its average content, and Sn content will be relatively high. After irradiation, Ag-In-Cd alloy will be single hcp phase when Ag content is between 55% and 61%.