Boiler is an important part of the Steam Power Plant. One of the combustion systems in the boiler is using the balance draft method, where combustion air conditions in the furnace supplied by Force Draft Fan (FDF), and residual combustion air (exhaust gas) are sucked with Induced Draft Fan (IDF) by maintaining the -30 Pa pressure furnace accordingly manufacturer's standard. Furnace has not been able to achieve ideal conditions, because the performance of Induce Draft Fan (IDF) has less optimal suction power. This is allegedly from the opening of the Inlet Guide Vane which is not yet optimal. The test model in the form of Induce Draft Fan is simulated using CFD modeling software. The dimensions of the inlet guide vane, rotor, and static blade are carried out by 3D scanning. While for the casing model uses the manufacturer's reference image. The results of this study are expected to improve IDF performance by determining the variation of the damper opening (IGV opening angle) optimally. From CFD simulation, pressure suction becomes more vacuum by opening the IGV from -10°, 0°, 10°, 40°, The value of the IDF pressure suction is -100 = -2494.7 Pa, 0° = -3129.5 Pa, 10° = -3398.2 Pa, 40° = -4425.2 Pa. Based on CFD simulations, the optimal damper opening is at 40°. At 41° opening of Inlet Guide Vane, the IDF suction ability decreases, This is indicated by the suction ability at -4249.4 Pa. Considering the process of setting the Inlet Guide Vane opening angle on the Induce Draft Fan requires a shutdown unit and production opportunities will disappear and the costs are relatively large, the performance optimization process is carried out using simulation.