After Mt. Merapi eruption, abundant of sediment was deposited in its slopes. In rainy season, the deposited sediment will be brought by discharge as debris flows. In order to reduce the negative impacts of debris flows, government constructed sabo works. Therefore, it is important to study effects of sabo works dimension on countermeasures debris flows. This study took Putih River as study case, which located on the western part of Mt. Merapi. SIMLAR V.1.0 software was used to simulate debris flow phenomena. Rainfall data was processed using Nakayashu method to obtain discharge for simulations. Topographical data as initial condition was used DEM with precision 20 x 20. Grain size of riverbed material was used from field. The simulations were conducted in three conditions, namely no sabo works, with sabo works in existing condition and modified dimension of sabo works. Result showed that in the simulation with no sabo works, debris flow velocity was relative high, so this condition was dangerous for inhabitant along the river. With sabo works in existing condition, debris flow velocity could be reduced, even though there were villages buried by sediment.