Proposed a capacitance measurement methods based on differential sampling in electrical capacitance tomography. An efficient oil-air-water three-phase flow measuring system was developed for small-scale separators based on the combination of the composite image re-construction method that was based on the Tikhonov’s regularization theorem and algebraic reconstruction and the two-phase flow measuring method that was based on the integration of the electrical capacitance tomography and the Venturi tube. The technology was successfully employed in petrochemical enterprises.