Disclosed is a method for preparing a stable fluid mixture by mixing hydrophilic and hydrophobic substances using ultrasound wherein homogeneous dispersion and mixing are possible so that dispersibility is greatly improved and separation between the hydrophilic and hydrophobic substances is minimized even after a long time. The apparatus for dispersing and mixing fluids by focused ultrasound includes a fluid storage unit for storing a fluid mixture of at least two fluids comprising a hydrophilic substance and a hydrophobic substance, the fluid storage unit comprising a first connector and a second connector connected to a fluid flow path such that the fluid mixture moves through a fluid flow path providing a portion through which the fluid mixture moves, a fluid dispersion unit for focusing ultrasound to a portion of the fluid flow path to disperse fluids contained in the fluid mixture by ultrasound when the fluid mixture moves the portion, and a fluid circulation unit for circulating the fluid mixture such that a portion of the fluid mixture relatively insufficiently dispersed is moved through the first connector from the fluid storage unit to the fluid dispersion unit and the fluid mixture dispersed by the fluid dispersion unit is moved through the second connector to the fluid storage unit.