The method of visualization and construction of 3D-refraction patterns in liquid volume is considered in this work. The research of transitional layer on the edge of the two liquids with the different optical characteristics is provided. The manual of the procedure for researching the diffusive layer by the laser refraction method is given. The developed algorithm and the program for modeling 3D-refraction patterns in the liquid volume allows to visualize the flat laser beam spreading in liquid. The 3D-refraction patterns for the different angles of the flat laser beam and numerous gradient index meaning of the lower layer is built.