The necessity of studying the nature of the propagation of laser radiation in the Anderson differential cuvette is substantiated in order to determine the optimal design parameters of a small-sized differential type refractometer. The construction of the Anderson differential cuvette is considered. A new method for studying the nature of the propagation of laser radiation in the differential Anderson cuvette is proposed. The trajectory of movement of the maximum of the laser radiation directive pattern in the cuvette, as well as beyond it (up to the sensor of the photodiode ruler on which the registration takes place) is plotted. An equation is obtained to study the changes in the nature of the propagation of laser radiation from various parameters of the differential cuvette, the reference liquid medium and the investigated liquid medium. A polynomial of the 12th degree is formed to obtain an analytical solution of the equation from the refractive index of the investigated medium.