Scale adhesion can often be seen at the contraction of hydraulic equipments in piping systems of power plants. Since the adhesion may affect the plant performance, the mechanism of this phenomenon is required to be clarified, and considerable prevention measures should take place for rational plant operation. In this study, scale adhesion experiments were conducted under high-temperature & high-pressure condition, to imitate the events at the actual contraction in power plants. Also the flow characteristics around the contraction were calculated numerically by adopting LES as a turbulence model. At points where pressure drop and wall shear showed maximum values, unique changes of adhered scale were observed. This may explain the relation of thermal-hydraulic and electro-chemical causes on contraction surface.