The present work is devoted to the new cylindrical cell based refractometer and its application methodology. In recent years chemistry, physics, medicine, human environment safety and protection and other areas have an increasing demand for accurate measurement of the concentration of the solution components, and the refractive index (RI) obtains the sensitive indication for this purpose. For the cylindrical cell based refractometer a new physical RI measuring method has been developed. The developed methodology employs a new criterion for determining the reading point of the refractometer, improving the unambiguity of the measurements results reading. The technique and calibration methodology to use the refractometers are developed to measure the composition of liquid. For the first time in the world resolution has been reached for the cylindrical cell based refractometer up to 10-5 RI, and mathematically proved possibility to measure RI with a resolution up to 10-7 The thesis consists of an introduction, 4 chapters and resume. It is written on 118 pages, contains 52 figures, 9 tables, 116 references and 10 appendixes. The work is written in English.