Abstract: An improved version of the method and instrument of solid-liquid equilibrium has been calibrated. The solubility of 2,6-dimethylphenol in cyclohexane was measured by this equipment and the data agree with literature values. On this basis, the solubilities of 2,4-dichlorobenzaldehyde in ethyl alcohol, acetone, acetic acid were measured accurately and correlated by UNIQUAC activity coefficient model. Those data can be used as the basis of selection of the process parameters in purification and crystallization of 2, 4-dichlorobenzaldehyde.