The aim of this project is to study the effect of mechanical structures on flood control of rainwater catchment systems in Taftan Catchments to identify the weak points and find a scientific approach to useful function of these mechanical structures. In this research , the capacity of the check dam reservoirs was calculated and measurements were laid in check dams reservoirs to determine the level of water in each flood. The result shows that the capacity of these mechanical structures is 145744m^2.  During this research, 4101090m³ precipitation have occurred that caused 939434 m³runoff in this area. The construction of these check dams reservoirs runoff has resulted in harvesting and infiltration of 320535 m³ floods although618899 m³of that have left this area. The period while the absence of these reservoirs, 939434 m³ runoff left this area and the destructive power of the floods were increased as well, that caused more erosion and less infiltration in main streams. Reviews show that the construction of these check dams reservoirs will reduce the amount of run off from 22.9 to 7.8 percentages. Before the construction of these structures, the record-high flood level was 145cm which reduced to 72cm after that. Statistical analysis of the data shows thatthere is a significant differenceat the 0.01 level (P<0.01) between the capacity of the flood before and after these constructions that means; the reduction of the flood in this study area