In this study, the oily sludge was extracted with toluene, naphthane, naphtha or petroleum ether as solvent to reveal the essential interaction in oily sludge through thermodynamic analysis method. The surface component activity (SCA) model was utilized to eliminate the particles accumulation effect (C-p-effect) in order to obtain evolutional Langmuir isotherm. The maximum adsorption capacity (Gamma(0)) of oil and equilibrium constant (K-eg) of desorption process was calculated from the slope and intercept of the linear fitted Langmuir isotherm. Hence, the thermodynamic functions, such as Gibbs free energy (Delta G), enthalpy change (Delta H) and entropy change (Delta S), were further determined from the results of K-eg. The Fourier transform infrared spectroscopy (FT-IR) was applied to analyze the oily sludge. Strong interactions, such as O-H center dot center dot center dot O hydrogen bond, between.oil molecules and particles were eventually found to be the essential reason for preventing the oil desorption. The thermodynamic analysis method developed in this work also provided feasible guidance to improve the extraction efficiency for oily sludge. (C) 2017 Elsevier B.V. All rights reserved.