Abstract: Control rods and absorption balls are very important and necessary part as the role of the power adjustment and the reactor on and off. In the simulator, it could occur that one grid cannot be full filled with control rods or absorption balls. In the design, grid for control rods and absorption balls will be increased which can improve the accuracy of the worth of the control system. The thicker grids will increase the computer time, so this method cannot be used in the simulator. In this paper, equivalent method was mentioned based on the absorption equivalent. The macro-section can be changed as the position of the control rods or the absorption balls, so the simulator can reflect the change of the control system. The result of this method is fit well with the result of the design, and it can be concluded that the application of equivalent method in simulator is well done.