The mechanism of the influence of ultrasound on the nucleation and growth of A2B6 nanoparticles in a colloidal solution was investigated. The proposed theory is based on an increase in the temperature of the colloidal solution and the diffusion coefficient of the monomer under the influence of ultrasonic cavitation. It was established that ultrasound leads to a decrease in the critical radius of colloidal nanoparticles. And when the radius of nanoparticles exceeds this critical value, their growth is observed. The dependence of the growth rate of CdSe nanoparticles on their radius at different temperatures and intensities of ultrasound was researched. It is shown that at the beginning of nanocrystal growth, an increase in intensity of ultrasound leads to an increase in the growth rate, followed by a sharp decrease. This makes it possible to synthesize colloidal quantum dots that are more uniform in size with the help of ultrasonic treatment.