We put forward a new expression of similarity between solute and solvent in terms of the cohesive energy for unlike molecules, which provides a quantitative measure of the principle that 'like dissolves like'. The investigation results indicate that as V-r (volume ratio) and SHSPR (the Square of Hansen Solubility Parameter Ratio) are far larger than unity (V-r >> 1, SHSPR >> 1), the similarity degree between solute and solvent is dominate by difference in molecular structure (size and interaction energy); as SHSPR approaches unity (SHSPR -> 1), the similarity degree is irrelative with molecular size, and it depends only on its deviation from ideal solution (positive or negative deviation). Its applications in water-solvent miscibility analysis, appropriate solvent selection for polymers and chemical products purification (liquid-liquid extraction and re-crystallization) have been verified with successful results. (C) 2018 Elsevier Ltd. All rights reserved.