To further understanding hydrophillic interactions of complex biomolecules at the microscopic level, an idealized polyatomic model-a square polyatomic sheet-is devised, which consists of positive and negative charges on atoms. In the framework of the extended RISM integral equation theory, we calculate the solvent-induced interactions between pairs of the hydrophillic polyatomic sheets in water. We find the total hydrophillic interaction (mean force) between two sheets in water is directly against the intermolecular force between these two sheets in vacuum. A further analysis reveals that the solvent-induced interaction is mainly attributed to the sheets-solvent interaction energy.