The invention discloses a method and a device for preparing nanoscale dispersion liquid. A hydrophobic compound is dissolved into an organic solvent as an organic phase, the organic phase, as more than one strand of liquid, and more than one strand of a water phase flow in a jet manner in a multi-inlet mixer cavity for continuous mixing to obtain mixed liquid, the mixed liquid flowing out of the cavity is continuously and circularly flown in the jet manner to return into the multi-inlet mixer cavity, and is then mixed with the organic phase and the water phase again, and the mixed liquid flowsout of a multi-inlet mixer until dispersion liquid with preset concentration is obtained, so that the nanoscale dispersion liquid is obtained. Nanoscale particles are quickly mixed and formed insidethe cavity once, the process of secondary particle formation caused by the fact that secondary attenuation mixing further needs to be carried out with a hydrophilic phase after flowing out of the cavity is avoided, and the particle size, distribution and stability of the dispersion liquid are improved; sufficiently large proportion water content and degree of supersaturation can be provided duringmixing through the application of recycle mixing, instantly uniform formation of particles is guaranteed, and meanwhile, the dispersion liquid is avoided from being excessively diluted due to an overlarge water proportion.