In this work, with the available solid-liquid equilibrium (SLE) data of six aromatic carboxylic acids, aromatic dicarboxylic acid isomers (terephthalic acid (TPA), isophthalic acid (IPA), and phthalic acid (PA)), and methyl benzoic acid isomers (m-toluic acid (m-TA), o-toluic acid (o-TA), and p-toluic acid (p-TA)) in acetic acid (HOAc) + water (H2O) solvent mixtures, the relationship between the molecular structure of the above aromatic carboxylic acids and the solubility of them in HOAc + H2O solvent mixtures is discussed. It could be found that among the aromatic dicarboxylic acid isomers and methyl benzoic acid isomers, TPA and p-TA have the lowest solubility in the same solvent and temperature, respectively. Meanwhile, three new groups, p-ArCOOH, m-ArCOOH, and o-ArCOOH, in the UNIFAC (Dortmund) model were first defined to distinguish the influence of the positions of ArCOOH on the thermodynamic properties of aromatic carboxylic acid isomers, which indicates that ArCOOH is located in the para, meta, and ortho positions of the ArCOOH or ArCH3 groups, respectively. Then, the interaction parameters of ArCOOH, p-ArCOOH, m-ArCOOH, and o-ArCOOH with other involved groups in the solvent systems are first obtained by regressing these available SLE data. By using the new defined group, the UNIFAC (Dortmund) model was used to correlate SLE data for the above ternary systems, and trimesic acid + HOAc + H2O systems agree with the experimentally measured results satisfactorily.